Instant, offset, and zone
An instant identifies one point on the timeline. A UTC offset describes a difference from UTC at that instant. A named region such as Europe/Paris represents a set of historical and future civil-time rules. These concepts should not be stored as if they were interchangeable.
Why date and location matter
Political bodies can change offsets and daylight-saving rules. A fixed +01:00 offset cannot tell an application whether a location will use +01:00 or +02:00 on a future date. Named-zone databases are updated to reflect these decisions, so deployed systems need current time-zone data.
Ambiguous and missing times
When clocks move backward, one local clock reading can occur twice. When clocks move forward, a range of local readings may not exist. Scheduling software should define how to resolve these cases and retain the intended named zone for recurring future events.
- Store event instants in an unambiguous form
- Retain a named zone for recurring civil schedules
- Display the zone, date, and offset to users
- Update system time-zone data
References and further reading
These primary or authoritative references support standards-dependent details. LipiCode’s explanations and examples are independently written for this workflow.