Daylight Saving Time Issues: DST Bugs to Avoid
Identify and fix daylight saving time bugs in software. Covers repeated hours, skipped hours, scheduling failures, and database timestamp traps.
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Tags: developer-tools, timestamps, dst
Daylight Saving Time Issues: Common DST Bugs and How to Avoid Them Daylight saving time produces some of the most surprising bugs in software. The transitions are infrequent enough that you may not notice a bug until it hits a user at 2 AM, and the symptoms are often subtle — one record off, a cron job running twice, a scheduled task that never fires. This article documents the bugs DST causes and how to structure your code to avoid them. --- What Happens During a DST Transition Most countries observing DST have two transitions per year. Spring forward (March in the Northern Hemisphere): Clocks move from 2:00 AM to 3:00 AM. One hour is skipped. Times between 2:00:00 and 2:59:59 do not exist on that date. Fall back (November in the Northern Hemisphere): Clocks move from 2:00 AM back to…
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