Good point. The answer is I don't know, I assumed that DateTime would handle that. It seems there is something relevant here https://metacpan.org/pod/DateTime::TimeZone#$tz-%3Eoffset_for_datetime(-$dt-)

Given a DateTime object, this method returns the offset in seconds for
+ the given datetime. This takes into account historical time zone inf
+ormation, as well as Daylight Saving Time. The offset is determined b
+y looking at the object's UTC Rata Die days and seconds.
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