The code used native date functions, this made tests not robust.
We switch to TYPO3 API to fetch the current date and time.
Test is adjusted to define the date and time to verify code works as
expected.
The property will always be set in the future.
We no longer can use it as an indicator.
We switch to freq as new indicator.
We also ensure that start has to be given for a single date.
Relates: #9892
