AT REST API

ActivityTimeline has its own API, it is switched off by default and can be turned on manually by ActivityTimeline Admin in ActivityTimeline Configuration->REST API:

It is possible to export list of all teams and users, their timeline schedules and list of custom events.
You can also create custom events on users' timeline using REST API (like bookings, holidays, vacations, etc).

The detailed documentation is available via the link below:
REST API