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/002194804280... http://www.shugiin.go.jp/internet/itdb_housei.nsf/html/houritsu/007195003310...
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. -- +--------------------------------------------------------+ HealthCare Relations Co., Ltd. 二階 隆幸 Nikai Takayuki 〒101-0054 東京都千代田区神田錦町3-13−7 名古路ビル本館1F TEL 042-485-7130 +--------------------------------------------------------+