What is the best practice for timezone conversions?

Question

I want to give users the option to change their timezone and display their data in that timezone. I'm currently storing a unix timestamp and would like to know what the best way to handle this conversion would be.

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I am storing my timestamp in unix format. My concern is what function can I use to do the conversion on the presentation layer?

Answer 1

Store date data as GMT, and in the user prefs let them store their timezone (which is simply an offset of GMT).

Answer 2

Keep everything as UTC in your data store and convert at your presentation layer.