I needed to write a similar service for our intranet to list the time at different installations world wide, knowing only their offset from UTC and whether or not they observe DST. DST occurs at the same time everywhere in the US, if it is observed.

I decided to just use one of the NIST time servers and a file with the offset, bool data

You can get the data by making a simple tcp call to the time server, which returns a string that you can split and compute the current time if you know the UTC off set.

Some more DST information, including what US territories, states and holdings acknowledge it.

C-.

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Flex the Geek