Incorrect historial DST rule for Hong Kong

李耀宗 lee_yiu_chung at
Sat Oct 24 04:39:33 UTC 2009

I found there are some mistakes for the historial DST rule for Hong Kong. Accoring to the DST record from Hong Kong Observatory (actually, it is not a observatory, but the official meteorological agency of HK, and also serves as the official timing agency), there are some missing and incorrect rules. Although the exact switch over time is missing, I think 3:30 is correct. The official DST record for Hong Kong can be obtained from

Mistakes I found:
- DST records before 1946 are missing (note: during 1942-1945 (WWII) Hong Kong is under Japanese occupation, and Hong Kong is put into DST for whole year, which would make HKT "in sync" with Japan. For 1941 you can assume the start/end time is 3:30, which should be a reasonale guess.
- The end date of 1952 end time is incorrect. The current tz rule implies the end date is Oct 26, but the actual end date is Oct 25.
- There is extra DST period during Dec 30 1973 to 20 Oct 74. (Yes, DST was applied during WINTER, probably for oil crisis.)
- No DST from 1980 onwards, but the current rule implies there was DST in 1980.

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