You could do that (look for a reliable source of timezone data) of course... but it's already been done twice: Date::Manip and DateTime. I wouldn't suggest that as a good idea to anyone not interested in the timezone problem itself.
There ARE perfectly valid reasons to reinvent this wheel (after all, I did just that with Date::Manip) but they are mostly about trying to improve the wheel, or learning how the wheel works. If that's you're level of interest... by all means, write your own timezone code. If you're not interested in the wheel itself (just need to use the data)... use one of the existing modules. The rules for Daylight Saving are way too complicated to do it yourself.
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