[tz] Japanese Summer time fallback transition in autumn 2020?

Paul Eggert eggert at cs.ucla.edu
Tue Sep 18 20:59:06 UTC 2018

On 9/18/18 1:43 PM, Paul Ganssle wrote:
> The law says that the last day of DST had 25 hours instead of 24. The
> question is whether in practice what happened was that starting 0:00 on
> Saturday, did people wait 25 hours (until 01:00 on Sunday) and THEN set
> their clocks back 1 hour, or did they wait 24 hours (until 00:00 on
> Sunday), and then set the clock back to 23:00?

Yes, that's the nub of the question. If people in Japan generally did 
the former, we should change tzdb to model the transition as one from 
01:00 to 00:00 Sunday; this is not exact but is the best we can do. If 
people generally did the latter we're OK as-is. Possibly some people did 
one thing while others did the other, as the American occupiers did not 
always see eye-to-eye with the Japanese populace and I doubt whether 
it's entirely a coincidence that Japan stopped observing DST three days 
after US occupation ended.

As we've already mentioned, old Japanese-language newspapers could help 
resolve this issue.

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