Dates and Time Zones in Production: UTC, timestamptz, DST, and Recurring Events That Do Not Drift

A practical guide to stop fighting with dates: why "store everything in UTC" is incomplete advice that breaks recurring events, the real difference between timestamp and timestamptz in PostgreSQL, what happens during daylight saving transitions (the hour that does not exist and the one that happens twice), zoneinfo and fold in Python, the Temporal API now standard in ES2026, why an index over AT TIME ZONE will not compile, how to keep tzdata current, and how to test all of it with hostile time zones in CI.

18 minutes read

Josue Puig

2026-09-10

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