A Primer on Daylight Saving Time in North America

[Don Boyer]

There's always some confusion when this comes up, so I thought I'd make one place to rant about it...    This is more for the benefit of people living outside of North America (specifically the US and Canada) and needing to know just how Daylight Saving Time occurs here, since most deck releases, Kickstarter projects, eBay auctions, etc. occur here and use our time conventions.

Almost everyone in the world is familiar with "Summer Time" or "Daylight Saving Time" (yes, it's "Saving", not "Savings" - it's not a bank account!).  Clocks go ahead in the spring by an hour, fall back in the fall by an hour.

In the US and Canada, most of those two countries observe Daylight Saving Time (DST), with the major exceptions being many Native American territories and the state of Arizona, which remain on Standard Time all year long.  Unlike the rest of the DST-observing world, however, our governments have seen fit to extend the duration of DST to the point where we're on Daylight Time more than we are on Standard Time, making it the de facto standard!  For most of the world that changes their clocks, they "spring ahead" in late March or early April and "fall back" some time in October - but seeing how special we are in North America, we start DST on the second Sunday in March and don't end it until the first Sunday in November.  Also, unlike in the European Union, we change time at 02:00 AM local time, with the change rolling from time zone to time zone - the EU mostly uses 01:00 UTC as the time to change across all EU time zones.  (At least that's what Wikipedia says, and I'm sticking to it!) 

And this doesn't even begin to touch the changes that occur on the southern half of the world!  But for the rest of the world, it's not much of an issue - in fact, the majority of the world DOESN'T observe DST or Summer Time.  Much of Asia doesn't use it, and most nations near the equator don't because they remain relatively unaffected by seasonal changes in relation to the duration of daylight per day.

But back to my point...  Here's how DST affects time in the most populous time zones in North America - Pacific (California, western British Columbia), Mountain (Colorado, Alberta), Central (eastern Texas, western Ontario) and Eastern (eastern Ontario, New York).  The UTC listing in the right column is the standard and is unaffected by Daylight Saving Time.

This year, the second Sunday of March is 10 March 2013 (a.k.a. tomorrow!).  All times shown in red are in Daylight Saving Time.

Pacific Time	Mountain Time	Central Time	Eastern Time	UTC
10:59:59 PM (Sat.)	11:59:59 PM (Sat.)	12:59:59 AM	01:59:59 AM	06:59:59
11:00:00 PM (Sat.)	12:00:00 AM	01:00:00 AM	03:00:00 AM	07:00:00
11:59:59 PM (Sat.)	12:59:59 AM	01:59:59 AM	03:59:59 AM	07:59:59
12:00:00 AM	01:00:00 AM	03:00:00 AM	04:00:00 AM	08:00:00
12:59:59 AM	01:59:59 AM	03:59:59 AM	04:59:59 AM	08:59:59
01:00:00 AM	03:00:00 AM	04:00:00 AM	05:00:00 AM	09:00:00
01:59:59 AM	03:59:59 AM	04:59:59 AM	05:59:59 AM	09:59:59
03:00:00 AM	04:00:00 AM	05:00:00 AM	06:00:00 AM	10:00:00

As the first Sunday in November is upon us - this year it will be 03 November 2013 - the reverse occurs.

Pacific Time	Mountain Time	Central Time	Eastern Time	UTC
10:59:59 PM (Sat.)	11:59:59 PM (Sat.)	12:59:59 AM	01:59:59 AM	05:59:59
11:00:00 PM (Sat.)	12:00:00 AM	01:00:00 AM	01:00:00 AM	06:00:00
11:59:59 PM (Sat.)	12:59:59 AM	01:59:59 AM	01:59:59 AM	06:59:59
12:00:00 AM	01:00:00 AM	01:00:00 AM	02:00:00 AM	07:00:00
12:59:59 AM	01:59:59 AM	01:59:59 AM	02:59:59 AM	07:59:59
01:00:00 AM	01:00:00 AM	02:00:00 AM	03:00:00 AM	08:00:00
01:59:59 AM	01:59:59 AM	02:59:59 AM	03:59:59 AM	08:59:59
01:00:00 AM	02:00:00 AM	03:00:00 AM	04:00:00 AM	09:00:00

For those of you noticing, that means the spring change day has only 23 hours, while the fall change day has 25 hours.  Believe me, when you work overnight shifts like I do, it makes a difference! 

Any questions?  Anyone wish to add info about how time changes occur where you live?

[Nurul]

British Summer Time (BST) takes effect on 31st March - 27th October I have nothing more to add

[Don Boyer]

British Summer Time (BST) takes effect on 31st March - 27th October I have nothing more to add

Does Great Britain have more than one time zone?  At what time does the change take place - is it all at once like the rest of Europe or by local time like the US?

[Nurul]

as far as I know, it's only the one timezone. It changes over at 1am.

[Don Boyer]

as far as I know, it's only the one timezone. It changes over at 1am.

As does the rest of Europe - at 01:00:00 UTC.

[agera94]

Thanks for the insight Don 

The Australia east coast has a weird daylight saving system. I live in the northern state called Queensland on the east coast. We don't have daylight savings, however, the three states below us (also on the east coast) do. Some people live near the border of Queensland and the state below us (New South Wales), and they work here in Queensland. Life must be so hard for them.

[MrMollusk]

THANK YOU SO MUCH!
I nearly forgot. Oh, jeeze I would have been screwed.

[Don Boyer]

Thanks for the insight Don 

The Australia east coast has a weird daylight saving system. I live in the northern state called Queensland on the east coast. We don't have daylight savings, however, the three states below us (also on the east coast) do. Some people live near the border of Queensland and the state below us (New South Wales), and they work here in Queensland. Life must be so hard for them.

Well, there's that hour shift that one way or another people on one side of the border who work on the other side have to account for, but most time zone changes of this nature are given boundaries in relatively low-population areas in order to affect fewer people.  Is that the case here?  I can't imagine that it's all that different for people commuting to/from Arizona, a Mountain Time Zone state in the US which doesn't observe DST.

To the south, Arizona shares a border with the state of Sonora, Mexico, which also doesn't observe DST due to economic ties to Arizona.  To the east (New Mexico) and the north (Utah and Colorado), most of the border communities are sparsely populated and many don't have a cross-border counterpart town/city within commuting distance.  To the west, the border is shared with Nevada and California, which are in the neighboring Pacific Time Zone - and because Arizona doesn't observe DST, it spends almost eight months of the year on the same time as those states when they are observing DST.  I'd say those community ties on the west of the state are the greatest reason Arizona ignores DST - they're far enough south that they shouldn't be seriously affected by changes in the duration of daytime on a day-to-day basis.

In cases where some kind of "hardship" would occur, most of the time the border between time zones simply gets redrawn - it's why the majority of Europe shares a single time zone, when geographically they should be much more divided.  France and Spain were at one time in the same time zone as Great Britain and Ireland - now they're part of the Central European Time Zone (CET).