Topic and Scope

Support ISO 8601 formatted strings such as in #1749. Closes #1749.

Concerns/issues

We might need to revisit this if someone decides to have timers with years, months, or days set. But this should be easy to extend.

Formal requirements

There are some formal requirements that should be satisfied. Please mark those by checking the corresponding box.

• I did check that the app can still be opened and does not throw any browser logs
• I created tests for newly added PHP code (check this if no PHP changes were made)
• I updated the OpenAPI specs and added an entry to the API changelog (check if API was not modified)
• I notified the matrix channel if I introduced an API change