[tz] Precise meaning of AT 25:00

Michael H Deckers michael.h.deckers at googlemail.com
Wed Jun 26 09:36:00 UTC 2019

On 2019-06-26 09:22, Stephen Colebourne asked:
> The Tokyo rule now includes the value 25:00 in the AT column. Can
> someone confirm the exact meaning of the 25:00? Is it
> a) an extended local time-of-day
> b) the actual duration from midnight at the start of day
> While similar, there would be a difference between the two definitions
> if there was a second DST gap/overlap earlier in the day.
> eg. imagine the case where DST starts at 13:00 (with a gap to 14:00)
> and ends at 26:00. With (a) the AT column would hold 26:00, while with
> (b) the AT column would hold 25:00
> I'm pretty sure it is (a), but wanted to double check before it gets
> baked into APIs
> Stephen

    Yes it is (a) because an AT value without suffix (or with

    suffix w) refers to the time in force just before the
    change in SAVE values. One could also write 25:00s
    for the AT value, referring to the time with SAVE
    value 00:00.


    Michael Deckers.

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