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

Phake Nick c933103 at gmail.com
Thu Sep 27 11:01:09 UTC 2018

I have found a bit more information on the topic.
In the webpage authored by National Astronomical Observatory of Japan
https://eco.mtk.nao.ac.jp/koyomi/wiki/BBFEB9EF2FB2C6BBFEB9EF.html , it
mentioned that using Showa 23 (year 1948) as example, 13pm of September 11
in summer time will equal to 0am of September 12 in standard time.
It cited a document issued by the Liaison Office which briefly existed
during the postwar period of Japan, where the detail on implementation of
the summer time is described in the document.

The text in the document do instruct a fall back to occur at September 11,
13pm in summer time, while ordinary citizens can change the clock before
they sleep.
* Note: despite the webpage being named as wiki, it is actually a
collection of information maintained by the Ephemeris Computation Office,
NAOJ, not something that can be edited by others.

2018-9-19 Wed 04:59, Paul Eggert <eggert at cs.ucla.edu> wrote:

> 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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