Question about time period transition points

Paul Koning paul_koning at
Mon Feb 14 19:44:23 UTC 2011

On Feb 14, 2011, at 2:39 PM, Adam Vartanian wrote:

>> Phrased differently, for the Americas/NewYork transitions this spring:
>> 1) Is the time coordinate value at the instant of transition "2:00 AM" or "3:00
>> AM" (NIST says "begins at 2:00 a.m. on the second Sunday of March")
>> 2) Is the designation of that coordinate (in the local New York City timezone)
>> "EDT" or "EST"?
> At least in the United States, time transitions from 1:59:59 AM EST to
> 3:00:00 AM EDT.  I don't know if other countries have different rules,
> but it would be surprising to me if they did.

The changeover time is just as much an arbitrary political decision as all the other aspects of DST change.  So yes, you can find a variety of changeover times.  You can find them in the "AT" column in the rules files.


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