At 09:24 -0700 2000-08-15, Thomas Carey wrote:

many locales undergo DST transition at midnight - for instance - on Thu 21 Sept 2000 19:30 - DST will end in Tehran, and local time will go from 00:00->23:00 (actually, from 23:59 to 23:00).

If "00:00 to 23:00" seems odd, you can say "24:00 to 23:00" - the change doesn't take a minute, it happens instantaneously. But just what time is it at that instant? Is that defined anywhere?

My question is whether this extra hour occurs (locally) on thursday or friday. I'd assume thursday, as 00:00 doesn't arrive before the transition.

can anyone confirm?

I can't confirm, but to me it would seem far stranger and more confusing to have periods from 23:00 to 24:00 both at the beginning and the end of the same day, than to have two lots of 23:00 to 24:00 consecutively within the same day. (I'm ignoring the question of the inclusivity or otherwise of the beginning and end instants of these periods.) --Alex -- _______________ Alex LIVINGSTON Macintosh and Lotus Notes Support / Information Technology (IT) Australian Graduate School of Management (AGSM) UNSW SYDNEY NSW 2052 / Australia Facsimile: +61 2 9931-9349 / Telephone: +61 2 9931-9264 Time : UTC+11---[last Mar. Sun.---UTC+10---[last Aug. Sun.---UTC+11--- At midday today, Wednesday, August 16, time since epoch (1-1-1 at 00:00:00) is 730347.5 days = 1999.62353779 average Gregorian years time until 3rd millennium, 21st century, 201st decade, 2001st year is 137.5 days = .37646221 average Gregorian years