# Time zones, all-day events and recurrence

Model instants, local dates and recurring events without silent assumptions.

Source: https://docs.getridian.com/concepts/time-and-series/
Language: en
Reviewed: 2026-09-20

## An instant needs an offset

Use an explicit UTC `Z` or numeric offset in API timestamps: `2026-10-25T10:00:00+01:00`. An IANA zone such as `Europe/Berlin` describes civil-time rules; it does not replace the timestamp's offset. Avoid ambiguous names such as “CST”.

## All-day is a local date

An all-day event is not always 24 elapsed hours. In Europe/Berlin, 25 October 2026 spans 25 hours because daylight saving time ends. Preserve the local date and use the intended calendar zone when comparing occupied intervals.

CalDAV live queries accept `timeZone` in MCP or `time_zone` in REST. If the calendar does not provide a usable zone, Ridian requires an explicit IANA zone instead of silently assuming UTC. Ask the user when the zone is unknown.

## A series is not a pile of independent events

A recurring series has rules and may contain moved or cancelled occurrences. Reading a range must account for those exceptions. Creating many separate weekly events does not create a native recurring series.

Ridian's MCP supports a bounded weekly-series creation path for Google and Microsoft. Read the exact `create_event` schema and supported recurrence fields in the [tool reference](https://docs.getridian.com/developers/mcp/). CalDAV can read existing series but does not support their creation, modification or deletion through this adapter.

## Use bounded windows

Event and availability queries are limited to 20 calendars and 31 days. Ask for the hours you need; a whole-week query includes nights unless you constrain it. For a dense calendar, use smaller windows rather than assuming a partial result is complete.