Scheduling integrity

Time zones & DST

Resolve local booking times safely across daylight-saving changes and compare the same instant across customer, staff and business zones.

Booking rule: store the real booking instant in UTC, retain the IANA time zone used to create it, and never silently guess when a local time is ambiguous or does not exist.

Same instant, different zones

One stored instant rendered for different viewers. This prevents calendar sync and reminder drift.

Required backend contract

PersistUTC instant + IANA zoneNever persist only a formatted local string.

Ambiguous timesAsk earlier or laterOccurs when clocks move backward.

Nonexistent timesReject and offer alternativesOccurs when clocks move forward.

Recurring seriesRe-resolve each occurrenceKeeps 09:00 local at 09:00 after DST changes.

DST resolution lab

Same instant, different zones

Required backend contract