Min hours daily per real day for all teachers

[Liviu Lalescu]

The meeting is an activity with (almost) all teachers and no students. My trick was to extend this meeting to a second hour. I think what you are suggesting is basically the same. 

Hmm... I think not the same. Say the majority of teachers have 1 hour of another activity and 1 hour from meeting this day, and the exception teachers have only 1 hour on this day. Then you can add a meeting activity with all the teachers, and n_exception_teachers dummy activities. Do you understand my idea?

[maxi_mus]

Yes, I understand. I don't think it makes a difference though (in this concrete example), because all the teachers that are available on Thursday will always have lessons anyway, so the dummy thing won't cause them to have too few lessons.

[Liviu Lalescu]

OK, but please also think of the gaps (there might appear one extra gap on Thursday).

[maxi_mus]

The second dummy lesson is immediately after the teacher meeting, and there is no more school then (the teacher meeting ends all students days anyway), so there cannot be additional gaps. But this is of course a hack that only works in this specific situation, which is why I was searching for an alternative.

[Liviu Lalescu]

Oh, I wrote the alternative in my posts above?

[Volker Dirr]

I am not talking about a gap between the teachers meeting. I am talking about gaps between for example the 2nd and the 4th hour that might be placed only, because the teacher meeting is "too long" if teachers have a max hours per day constraint.
If you are using a max hours per day constraint for teachers and if you make the meeting longer, then this will force FET to produce gaps in teachers timetable and this also mean FET is forced to fill this gaps by other teachers and this mean FET will be forced to place gaps between that filled hours and the teacher meeting.
So if you use a teachers max hours per day constraint and you make the meeting "longer", then you will get probably much more teacher gaps.