Max one history lesson on 6th-7th position in each class (solution 1)

For each subject you can define how many times it is allowed to be on question marked positions.
At first, define these questionmarked possitions in "Time-off" for subject.

Then you can set, how many lessons is allowed.

Typical usage of this feature is the following:

Imagine the class has 3 lessons of history per week. It will probably not be possible to have ALL three lessons before lunch for all classes. But it will be very bad if ALL 3 lessons are after lunch. Then the teacher can complain that he cannot teach history in that class.

So you can specify that e.g 6th and 7th period are question marked and that you accept only one lesson on these question marked position in each class. Then the software will respect only those timetables where all three lessons are before lunch or where 2 lessons are before and only one is after.

Notes:
the above is set for ALL lessons of this subject.

If you need different settings for different classes you can use one of these options:

Specify how many lessons shall be before certain position

Max one history lesson on 6th position in each class (solution 2)