Where do I find it?
Configuration > Transportation > Timetable
What does it mean?
Timetable is where you can set for how long a created timetable should be valid (for example if you want seasonal timetables) and the departure times of your different tours.
What should I do?
Specify the duration of your timetables (maybe for a season or several years). Then press on the created timetable and create a schedule for your tours with the specific departure time.