Glossary

VTIMEZONE

The iCalendar component that embeds timezone rules so event times survive daylight saving changes.

A VTIMEZONE block ships the timezone's rules (standard time, daylight time, and when they switch) inside the calendar data itself. Events reference it so a 4pm practice stays 4pm local, on both sides of a daylight saving transition, in every app.

Feeds that omit VTIMEZONE and publish raw UTC times often look right until the clocks change, then drift by an hour. It is one of the most common causes of a calendar being mysteriously off in March and November.