If you receive the message that changes to the timetable have been detected and a new period should be created, you have two options:

1. The changes apply from a point in time in the future:
Create a new period. The changes are then only displayed from the start date of the newly created period.

2. The changes have also applied in the past and have only now been saved in the timetable:
Overwrite the timetable.
In this case, the change is also displayed in the past timetable.
This also applies to substitutions that have been entered for the past.