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Exceptions, Oddities and Notes

What is GMT?

Time zones are offset from Greenwich Mean Time (GMT). For example, Eastern Standard Time (EST) is "GMT‑5", which means it is five hours earlier than GMT.

Greenwich Mean Time is referred to in different ways, usually GMT, UTC (Coordinated Universal Time), or Zulu time. Military and Aviation use Zulu, or just Z.

At we use GMT, because that is what travelers seem most familiar with. Time geeks (they walk among us) prefer you use UTC. And truly there are small technical differences between UTC and GMT, but they do not impact travelers.

Time zones are fundamentally based on 24 imaginary wedges running from pole to pole at 15 degree increments, starting at the Greenwich Meridian (also called the Prime Meridian), Greenwich Meridian
Click where your mouse is hovering to view a larger image
a line between the north and south pole along longitude 0°. It passes through the Royal Observatory in Greenwich, England - thus "Greenwich Mean Time".

Starting with an offset of zero hours for that first "slice" (which occupies the longitude from ‑7.5° to +7.5°) heading into the Eastern Hemisphere, for each 15° wedge you add 1 hour. Heading into the Western Hemisphere (towards North America) you subtract 1 hour for each wedge. They meet on the other side of the globe at 180° longitude, the fundamental basis of the International Date Line.

Actual time zone borders deviate (often radically) from this fundamental basis. Politics, history, commerce, and sometimes forces that defy rational explanation all combine to influence time zone borders.

The International Date Line itself is similarly influenced, following a ragged path roughly centered at 180° longitude. Crossing it traveling eastward you subtract 24 hours, and if traveling westward you add 24 hours. Unless the part of the date line you just crossed happens to coincide with a time zone border, in which case you also add or subrtract an hour. Simple :)

Most time zones are offset from GMT in whole hour increments. A few are offset in fractions of an hour -- most of those by half hour, a few by a quarter of an hour. There is only one such exception In North America: the Canadian island of Newfoundland is offset on a half hour boundary (GMT‑3:30 during Standard Time).

Forward thinkers want to end the madness. Click here to see their their elegant solution.

There are 9 time zones in North America. Being in the Western hemisphere, they are offset from GMT in negative increments:

  Hawaiian/Aleutian Alaska Pacific Mountain Central Eastern Atlantic Newfoundland Pierre
Standard Time


‑3:30 (really)
Daylight Saving Time



‑2:30 (I swear)

Understanding exceptions

Near official time zone borders, there are sometimes unnoficial exceptions where locally observed time differs. The main borders in normally follow the observed time - which is what a traveler is likely to actually encounter.

Unofficial "observed" differences usually follow vague areas of economic or political influence which defy precise definition. But we had to draw them somewhere. Often these borders are in lightly settled areas. We took pains to draw them on the correct side of roads, businesses, services and populated settlements. That was our intent anyway - corrections appreciated!

Wherever these areas are in the US, unofficial borders are drawn in lime green, with the official alternative drawn in dark green. No attempt was made to do this for other countries, because distinctions between official and unofficial blur a bit in the various political subdivisions. In the US all official time zone borders are well and clearly documented by a single source - the US Dept. of Transportation.

Within an area where observed practice differs from official, there are often internal exceptions. Possible examples are polling places, post offices or other federal offices -- and sometimes law enforcement or various other governmental entities which may observe official time.

Bars or liquor stores in these areas are often required by law to observe official time. This can provide quite an advantage for properly situated bars, when last-call sojourners migrate across an official time zone border to cadge one more hour of bliss.

Here are the exceptions that made their way into the boundaries at


NV: In northern Elko County Nevada Jackpot, Jarbidge, Owyhee, Mountain City, and the Duck Valley Indian Reservation all observe Mountain time though they are officially in the Pacific time zone.

NV: West Wendover Nevada is officially in the Mountain Time zone.

OK: Kenton Oklahoma observes Mountain time though they are officially in the Central tim zone.

NM: Nara Visa New Mexico observes Central time though they are officially in the Mountain time zone.

TX: Guadalupe Mountains National Park and the surrounding area of the NW Corner of Culburson County observes Mountain time though all of the county is officially in the Central Time zone. Even the National Park observes Mountain time, an oddity itself in that federal facilities rarely follow local unnoficial exceptions. This exception is so firmly entrenched in the area that it is widely mistaken as official. The distance to which the observance of this exception extends south and east of Hwy 180 is arbitrary. That part of the county is sparsely populated and appears to have no services, so the point is somewhat moot.

AL: Phenix City Alabama (no, that's not a typo... though it may have started out that way - but maybe not) and the area witin a 10‑15 mile radius on the AL side of the state border observes Eastern time, even though they are officially in the Central time zone.

AL: Valley/Lanett Alabama and the area within a 10‑15 mile radius on the AL side of the state border observes Eastern time even though they are officially in the Central time zone.

AK: Hyder Alaska unofficially observes Pacific time in sync with Stewart Canada, its neighbor to the east., even though they are officially in the Alaska time zone. But the post office, being a federal facility, remains on Alaska time.

AK: In November 2015, the Annette Island Indian Reservation near the southern tip of Alaska ended a long standing official exception which had it observing GMT‑8, the same as Pacific Standard time, year round. Prior to 2015 it did not observe Daylight Saving time, aligning it with British Columbia in the Winter, and most of Alaska in the Summer.

SD: The city of Fort Pierre South Dakota (legally in the Mountain time zone) and a large radius on the west side of the Mountain/Central border observes Central time. Research determined that the distance this observance extends to the west is a matter of disagreement among the locals. After some effort to get a definitive answer I gave up and arbitrarily selected 20 miles, though I heard credible opinions that it stretched out as much as 50 miles. There are no services and very few residents in the western part of Stanley county, so the point is somewhat moot.

CA: Winterhaven California, in deference to its proximity to Yuma AZ, observes Mountain Standard Time year round. This means that (like AZ) Winterhaven does not observe Daylight Saving time. So this puts Winterhaven ahead of California by one hour (in sync with Arizona) during Standard time - in the Fall and Winter. And in sync with both CA and AZ during Spring and Summer (Daylight Saving time). The dividing line of this observed boundary is locally considered to be the border of the Fort Yuma‑Quechan Indian Reservation.

CA: Earp/Vidal California, in deference to its proximity to Parker AZ, observes Mountain Standard Time year round. This means that Earp and the surrounding area does not observe Daylight Saving time. So this puts Earp ahead of CA by one hour (in sync with AZ) during Standard time - in the Fall and Winter. And in sync with both CA and AZ during Spring and Summer (Daylight Saving time). The dividing line of this observed boundary is estimated, but it is reported to extend to somewhere between Vidal and Vidal Junction.

Saskatchewan: Two things are odd about the time in the province of Saskatchewan. Firstly, it observes Central Time instead of the Mountain Time Zone in which most of it geographically resides. Secondly, it does not observe Daylight Saving time, remaining on Central Standard time (GMT‑6) year round. There are a couple of exceptions in border areas - see below.

Saskatchewan: The western city of Lloydminster area, which straddles the provincial border with Alberta, officially observes Mountain Time including Daylight Saving time

Saskatchewan: The eastern towns of Denare Beach and Creighton which are near the provincial border with Manitoba, observe Daylight Saving time in order to remain in sync with the Manitoba town of Flin Flan.

British Columbia: The Peace River Regional District (a large chunk of east‑central BC) observes Mountain Standard time year round, and does not observe Daylight Saving time. This includes Dawson Creek, Fort St. John and the surrounding area. So in Spring/Summer they are in sync with the rest of BC (which observes Pacific Daylight time). But in the winter they instead sync up with their neighbors to the east in Alberta. (NOTE: In November 2015, the "Northern Rockies Regional Municipality", which sits just north occupying the northeast corner of BC, will change its time observance to match the Peace River area. Interestingly, this observance may itself be an error: "In a 1974 referendum vote, Peace River Regional District communities voted to change their time zone to Mountain Standard Time all year round. The referendum had four options on it, including Mountain Standard Time and Mountain Standard with Daylight Savings Time. According to local historian Larry Evans, most residents wanted the second option, but accidentally voted for Mountain Standard Time without Daylight Savings Time."

Quebec: The eastern end of Anticosti Island, and that portion of mainland Quebec laying north of the island and west of the Natashquan river, now officially observe Eastern time.

Ontario: Southern Ontario, west of Thunder Bay, an area including Upsala, Shebandowan and Atikokan locally observes Eastern time even though they lie in the Central time zone. Also, the Atikokan portion of this area, including Quetico Provincial Park, does not observe Daylight Saving time, though in some descriptions they are said to observe Central Daylight time year round - which is the same thing in wall clock time.

Ontario: The towns of Pickle Lake and New Osnaburgh do not observe Daylight Saving time.

Ontario: The "Big Trout Lake" area observes Central time. The border is drawn by estimate.

Nunavut: Though the community of Arctic Bay on the western edge of Baffin Island is technically in the Central Time zone, it observes Eastern time to keep in sync with the bulk of the island.

Nayarit: This Mexican state is in the Mountain time zone, but in April 2010, Bahia de Banderas at its southern tip officially shifted into the Central time zone to sync up with Puerto Vallarta across the border in the state of Jalisco.

Other oddities:

Canada, Newfoundland:

  • Another Newfie related tidbit: Because the eastern bit of Quebec does not observe daylight saving time, during DST the 20 mile ferry ride from Newfoundland to Quebec involves changing your watch an hour and a half. Just half an hour in Standard time.
  • One last thing: Just off the tip of Newfoundland's Burin Peninsula sit the islands of St. Pierre and Miquelon. These are French holdings. Not French Canadian, French. They have their own time zone, "Pierre & Miquelon Time", which is one hour later than the Atlantic Time Zone, putting it half an hour later than Newfoundland.

    So if you are planning to take the ferry don't forget that the island ferry terminal in Saint‑Pierre is half an hour later than the Newfoundland terminal in Fortune.

The Aleutian Islands of Tommorow (or yesterday?)

  • The westernmost few islands in the Aleutian chain actually push the Hawaiian/Aleutian time zone a few degrees west of the 180 degree line. Not to worry - the powers that be nudged the international date line out of the way so all of Alaska is on the same side of the date line, along with the other 49 states.

Daylight Saving Time (explained!)

Note: Frequently referred to as Daylight Savings Time, which is incorrect. It's "saving", not "savings".

In the movies, the major blockbuster action thriller "Daylight Saving" was based on the hidden drama behind Daylight Saving Time. Click here to watch the amazing trailer.

US and Canada: DST starts 2AM the second Sunday in March, and ends at 2AM the first Sunday in November.

Our data presumes that by default most North American locations follow DST (not necessarily on the same schedule). Exeptions are discussed below:

  • Meanwhile, back in the desert: Even though Arizona does not observe Daylight Saving Time, the Navajo Indian Reservation (which takes up most of northeastern AZ) does observe DST. To add to the confusion, the Hopi Indian Reservation, which is wholly enclosed within the Navajo Reservation, does NOT observe DST. Confused? We're just getting started.
  • Consider also that the Navajos have an enclave containing the village of Jeddito, entirely within the Hopi reservation. And that the Hopi reservation has an exclave at Moenkopi, just south of Tuba City. Still not confused?
  • Some of the businesses in Tuba city (within the Navajo Reservation) reportedly do not observe Daylight Saving time, so as to avoid confusing the tourists. Good luck with that. At least that puts them in sync with their Hopi neighbors across highway 160 in Moenkopi. Got it?
  • The Navajo National Monument and the Canyon de Chelly National Monument both lie within the AZ portion of the Navajo Indian Reservation.  , and follow Navajo time instead of AZ time, so they do not observe DST.

    While traveling in this part of Arizona, do not presume that your cell phone is going to get it right, especially if you have poor service.


  • The Dangling Rope Marina lies on Lake Powell a few miles north of the AZ/UT border.  It does not observe DST

Hawaii does not observe Daylight Saving time.

Indiana: As of 2005, the whole state observes Daylight Saving time. Prior to that only parts of the Hoosier state observed DST.

Newfoundland/Labrador: As of the Spring of 2011, Newfoundland officially shifted their Daylight Saving Time transition to 2AM. Prior to that Newfie DST started and ended at 12:01 AM, 119 minutes earlier than the rest of Canada and the US. So before 2011, when Newfies returned to Standard Time in the Fall, at one minute after midnight Sunday morning they not only changed time, they changed date - reverting back to 11:01PM Saturday. I can't imagine why they did that, but I am fairly certain the computer geeks were not consulted.

St. Pierre and Miquelon: These islands off the coast of Newfoundland are French, and thus part of the EU. They have their own time zone. However, they follow Canadian DST date and time observance, not EU (European Union) dates and times, which are different.

Mexico: Mexico starts DST at 2AM on the first Sunday in April (3 or 4 weeks before the US), returning to Standard time at 2AM on the last Sunday in October (one week before the US). This causes a temporary difference between US and Mexican time even in the same time zone.

Mexico: The state of Sonora does not observe DST at all, in sync with Arizona - its northern neighbor.

Mexico: In 2015 the state of Quintana Roo (think Cozumel and Cancun) changed from Central time with Daylight Saving observance, to Eastern Standard Time year round, with no Daylight Saving. This takes them from GMT‑6 (CST)/GMT‑5(CDT) to full time GMT‑5(EST).

Mexico northern border: In 2010 Mexico officially changed the DST schedule for certain areas on or near the northern border to follow the USA schedule.  The affected area is defined by municipalities, which are similar to US counties.  Municipalities often (but not always) have the same name as the city which is the Municipal Seat.  Here is the list of affected states and the included municipalities:

Baja: All of Baja (five municipalities). No part of Baja Sur is included.


  • Juarez
  • Ojinaga
  • Ascension
  • Coyame del Sotol
  • Guadalupe
  • Janos
  • Manuel Benavides
  • Praxedis G. Guerrero
  • Ademas Acuna
  • Piedras Negras
  • Guerrero
  • Hidalgo
  • Jimenez
  • Zaragoza
  • Nava
  • Ocampo
Nuevo Leon:
  • Anáhuac
  • Los Aldama
  • Nuevo Laredo
  • Reynosa
  • Matamoros
  • Camargo
  • Guerrero
  • Gustavo Díaz Ordaz
  • Mier
  • Miguel Alemán
  • Río Bravo
  • Valle Hermoso

Mexico/Oaxaca: Most municipalities in the southern Mexican state of Oaxaca refuse to honor DST. This is an ongoing dispute with their federal government and may change. These Oaxacan DST exceptions are not documented and thus are NOT reflected in the data.

Some North American Amish communities opt not to observe DST, which they call "English time" or "Fast time", opting instead to follow "slow time" (Standard Time) year round. These Amish DST exceptions are not documented and thus are NOT reflected in the data.

Central American countries including Belize and Guatemala which are on Mexico's southern border, do not observe Daylight Saving time. Thus, in the Summer time (DST), there is a time transition between Mexico and it's southern neighbors - reflected in light blue on the map. The next time zone to the south is the Central/Eastern time zone border between Panama and Costa Rica. Because neither observes DST, the time transition at their border is year‑round and remains drawn in magenta. So during DST, departing that that portion of Central America north of Panama you jump forward an hour no matter whether you are heading north into Mexico, or south into Panama.

Caribbean and Central American islands (we concern ourselves only with those in the Eastern and Atlantic time zones) have a mix of DST observance, and the situation sometimes changes with little notice. Cuba, the Bahamas currently observe DST. As of this writing the Cayman Islands are studying a possible shift to observe DST.  The Turks and Caicos Islands have their own erratic relationship with DST, scroll down a little to get the latest.

Cuba has been changing their clocks on the same dates as the U.S., etc., since 2013, but their changes happen at midnight standard time -- midnight CUST(EST) & 1 AM CUDT(EDT).

Though Bermuda is not technically part of North America, and is well north of the Caribbean, it is worth noting that it also follows DST, on the US/Canada schedule.  It is in the Atlantic time zone.

Turks and Caicos (a Carribean island nation just east of the Bahamas) ceased observing DST in 2015  by shifting from the Eastern time zone with a DST observance - to the observing Atlantic Standard Time full time. The last time they changed their clocks was in March 2015, though technically the actual policy changed in November 2015, when they did not set their clocks back. This takes them from GMT‑5 (EST)/GMT‑4(EDT) to full time GMT‑4(AST). This means that only in the Spring/Summer will they be in sync with the Bahamas and Cuba, their Western neighbors. But they will be in sync year round with the Dominican Republic and Puerto Rico, their neighbors to the South. This change was originally planned for November 2014 but the government postponed it one year.

But wait, the plot thickens. In July 2017 the government issued a poorly worded announcement that seems to suggest they will resume DST observance in 2018.

Haiti has an erratic history of DST observance and a pattern of changing observance policy with almost no notice.

They observed DST from 1983‑1997, 2005‑2006, 2012-2015, and began again in 2017.

Announcements of the policy change in 2012, 2016 and 2017 were made at the last moment.  The 2017 announcement was made Friday March 10 2017, taking effect on Sunday March 12.

European Union: Though outside our area of focus, it is useful to keep in mind that the EU differs from the US and Canada by observing DST from the last Sunday in March to the last Sunday in October. All EU countries shift at the same moment (1AM GMT) no matter what time zone that country observes.

More Notes

The borders in were drawn primarily for road travelers. Less effort is made for precision over roadless areas or over water. The specific time zone needs of offroad travelers, aviators or mariners are beyond our scope. We do strive to keep borders on the correct side of all islands and remote settlements.

Wherever the real time zone border follows an irregular boundary such as a river or a ridge we do not try to exactly reproduce the boundary - which takes too many data points. Instead we simplify the line while not letting it touch or cross any roads except at the correct points where that road actually does cross or touch the real time zone boundary. So it may look a bit "low res" when you are zoomed way in, but there (hopefully) should be no instances where any part of a road is on the wrong side of a time zone border line.

For a description of just how difficult dealing with time zones can be, watch this youtube video. It will make you laugh, and leave you sympathetic to those who need to worry about such things.

Acknowledgements, Credits and Thanks

© 2010-2021 Steve Jones. All Rights Reserved.

DISCLAIMER: All content was generated via human effort. Every attempt is made to ensure accuracy, and any errors detected or reported are corrected. But it is not possible to guarantee 100% accuracy. Therefore the contents of this site are not suitable for any use involving risk to health, finances or property.

DO NOT ASSUME ONTIME ZONE BORDERS REFLECT POLITICAL BOUNDARIES. Some political boundaries are complex, with conflicting sources of data and possible ongoing disputes. This is especially true of many Native American lands. OTZ boundaries seek only to show the likely time at a given location, not to indicate anything about the local legal or political authority. Travelers should use other resources to remain mindful of their location when near international boundaries or those of soverign entities, especially those which may be poorly marked or follow geographic features.

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