Evan Dodds - Microsoft Exchange Server Blog

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Hooray for Eastern Standard Time!

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Well, I'm back from vacation and thanks to this morning's time change (at least in the US), very glad to be back into Eastern Standard Time! Warning: Timezone misunderstandings are a huge pet peeve of mine. Ask my friends. :) 

This is the easy part of the year -- the half of the year where no matter how little someone understands timezones, they can blithely state that the meeting is at "2pm EST" or that they work "8-5 EST" and actually be right! During Daylight Saving Time (essentially, April -> October in the US), lots of people I interact with still refer to Eastern Standard Time, totally oblivious to the fact that they are referencing a different timezone than they're currently in.

So, here's the short version -- a pocket guide, if you will:

  • Greenwich Mean Time (GMT/UTC) is a fixed timezone. It never changes.
  • Eastern Standard Time (EST) is also a fixed timezone. It is (always) GMT-5:00.
  • Eastern Daylight Time (EDT) is also a fixed timezone. It is (always) GMT-4:00.

In (most of) the US, we simply jump back and forth an hour twice each year -- we switch into a different timezone. EST is always 5 hours behind GMT. EDT is always 4 hours behind GMT.

And here's the important thing: If you say the meeting is at 2pm EST... during July.... in Charlotte, NC... do you mean that we should show up at 3pm EDT? Should I just assume you don't understand timezones when I put the meeting into my Outlook calendar with a 2pm EDT start time? Computers understand timezones, of course!

See these links for additional information:

  • http://wwp.greenwichmeantime.com/time-zone/rules/usa.htm
  • http://wwp.greenwichmeantime.com/info/daylightsaving.htm
  • http://www.boulder.nist.gov/timefreq/general/misc.htm#Anchor-32566
  • http://webexhibits.org/daylightsaving/

    (this post dedicated to Michael, Scott and Jodi - who get to listen to me rant on this topic at least twice each year). :)

    Updated Jan 17, 2005 – I’ve written a utility that’ll tell you how your machine’s timezone settings are configured. This won’t tell you which timezone you’re in (that’d be a neat trick!), but it’ll tell you which timezone your machine is currently configured for plus all the DST stuff. Get it here.

  • Comments
    • Don't call it GMT - it just confuses us poor Brits (who will happily refer to GMT between April and October, when they should refer to BST, British Summer Time). We normally switch to BST a week before the US switches to daylight savings, but switch back on the same date (although not at the same time!)

      Actually a number of problems in UK-developed software arise from the fact that e.g. DateTime.Now and DateTime.UtcNow return the same result for six months of the year. Developers forget that for the other half, they don't.

    • Mike - Exactly my point! Sorry to hear it's not just we in the US who are clueless. They should teach this stuff in the schools. :)

    • Great show for you we are using some new Audio gear to improve the quality. Time to in the can...

    • Now if we could just stay on EDT all of the damn time in NA then it wouldn't be dark at 4:30 pm and light at 7 am.... I don't mind going to work in the dark, I do mind getting home in the dark.


      Hell I woudl rather the sun came up at 9 am and set at 7 pm than the way we have it now. Then at least I would have time to play outside after work!

    • LOL! Now take into account those places such as Arizona and Indiana that NEVER switch time. They jump timezones (Eastern Standard time to Central Daylight Time in Indiana). I used to live in Indiana, and while I think it's nice to never have to worry about changing all the clocks in your house, I understand that places such as the airport have nightmares about Daylight Savings.

    • I think you are missing the forest for the trees here. You are probably one of those technically succint folks who celebrated the millenium in 2001 ;)

      While you are absolutely correct in your understanding and explanation of the issue, you should probably take into account that the vast majority of people in the US don't take into account the distinctions you make regarding EDT vs EST. Just treat the rest of us like the fools that we are and indulge our ignorance.

    • So far, this post has been the best in the whole blog ;)

      /Siddharth

    • Simply amazing how the most trivial small facts escape so many people.

      It almost resembles the odd linguistic drift in cliche phrases you hear from people I can only assume are pre-literate or something. Having never shared in our culture through reading, they come up with howlers like "hone in on" when they mean "home in on" and so forth.

    • If you read my post back in October, you already knew to set your clock ahead this morning. That’s...

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