[tz] The Japanese time zone rule is wrong.

[二階隆幸]

Hello, I'm Takayuki Nikai.

I will report mistakes in Japanese time zone rules.
Under Japanese law the daylight savings time boundary is written as 0:00, but tzdata is defined as 2:00.
Also, the end of daylight saving time is Sunday, not Saturday.

The source of information is Japanese law.

   http://www.shugiin.go.jp/internet/itdb_housei.nsf/html/houritsu/00219480428029.htm
   http://www.shugiin.go.jp/internet/itdb_housei.nsf/html/houritsu/00719500331039.htm
   > 四月の第一土曜日の午後十二時から九月の第二土曜日の翌日の午前零時までの間
   > 第一条及び第二条第一項中「四月」を「五月」に改める。

In summary, it is written as follows.
 From 24:00 on the first Saturday in May,
Until 0:00 on the day after the second Saturday in September.

However, in Time Zone Database (2018a (Released 2018-01-12) which is currently distributed, it is starting from 2:00 as follows and it is wrong.

   # Rule  NAME    FROM    TO     TYPE IN     ON      AT      SAVE    LETTER / S
   Rule    Japan   1948    only   -    May    Sun>=1  2:00    1:00    D
   Rule    Japan   1948    1951   -    Sep    Sat>=8  2:00    0       S
   Rule    Japan   1949    only   -    Apr    Sun>=1  2:00    1:00    D
   Rule    Japan   1950    1951   -    May    Sun>=1  2:00    1:00    D

I think that it will be correct as follows.

   # Rule  NAME    FROM    TO     TYPE IN     ON      AT      SAVE    LETTER / S
   Rule    Japan   1948    only   -    May    Sun>=1  0:00    1:00    D
   Rule    Japan   1948    1951   -    Sep    Sun>=8  0:00    0       S
   Rule    Japan   1949    only   -    Apr    Sun>=1  0:00    1:00    D
   Rule    Japan   1950    1951   -    May    Sun>=1  0:00    1:00    D

An error will occur in past date time analysis.
Please consider modification.
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