Time, Dates, and Time Zones

Time data answers two different questions. An instant answers when something happened on a shared timeline. A local date and time answers what a clock and calendar showed in a place.

Keep those questions separate. An audit event, log entry, and completed payment need an instant. A meeting at nine in Rome or a recurring business cutoff needs local calendar meaning as well.

The basic model

UTC is the shared reference used by Internet timestamps. A UTC timestamp such as 2026-07-22T14:00:00Z identifies one instant. The Z means a zero offset from UTC.

A UTC offset is a number such as +02:00 or -04:00. It states the difference between a local clock and UTC at that instant. It does not state the rules for that place tomorrow.

A time zone is a named rule set for a place or region. It maps an instant to a local date, local time, and offset. The IANA Time Zone Database supplies names such as Europe/Rome and records offset and daylight-saving changes for representative locations.