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#dst

2 stories

Banner: world clocks with one clock jumping forward an hour across a daylight saving boundary

Programming Languages

Timezones for developers: UTC instants, IANA zones and DST traps

Daniel Tran · Mar 11, 2025 · 9 min read

A practical guide to time handling that survives DST switches: when to store UTC instants, when to keep local time plus an IANA zone, how gaps and overlaps behave, which database types to use, and how to test with fixed clocks.

Incidents & Postmortems Bug Report

Nightly billing job ran twice on the DST fall-back night and double-charged customers

Daniel Tran · Nov 4, 2024 · 9 min read

On November 3, 2024, our 01:30 billing run fired at 01:30 CDT and again at 01:30 CST, charging 1,284 subscriptions twice. The in-house scheduler matched local wall-clock time. We moved schedules to UTC and added idempotency keys, a run ledger and a unique constraint.