What’s wrong with calculating the exact UTC time the event is starting and storing only that?
The problem is that we are losing crucial details about the event creator’s original intent.
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My strong recommendation here is that the most important thing to record is the original user’s intent. If they said the event is happening at 6pm, store that! Make sure that when they go to edit their event later they see the same editable time that they entered when they first created it.
Simon Willison
Storing times for human events (Simon Willison’s Weblog)
Scott Boehmer 