How to ensure that teacher starts teaching with 1st or 2nd period (he cannot start later than 2nd)

You can add this advanced cardrelationship:

Notes:
- you can select the teachers and select only the teachers that have enough lessons
- as usual: add this constraint only when you can already generate the timetable without it
- in some timetables this constraint might not work, when you for example have much more teacher's than classes there will not be enough early positions to place all the teachers