Time Zone Reference

Why zone names, not offsets

"UTC+05:30" identifies an offset; Asia/Kolkata identifies a place with a history. That distinction matters because offsets change: zones adopt and abandon daylight saving, and occasionally shift permanently. The IANA identifier carries every one of those changes, so a timestamp from 1995 converts using the rules that were in force in 1995.

Store the zone identifier alongside any date a user entered in local terms. Storing only the offset means you cannot correctly re-render that date after the next rule change — and rule changes happen several times a year somewhere in the world.