Thanks a lot!

A few answers:

I put all constraints manually (that is why it took me so long to finish).

I experimented that putting a space constraint to a group of students did not work for activities, I don't know why.

All space constraints are somehow mandatory as some classes have their own room (single constraint ore double for the possibility to use a pc lab) and others tour the whole school... plus the ones that tour are the only ones that are sent in the second building and these decisions were made by the council so I cannot avoid them.

The current number of placed activities looks stable after a few minutes, then it raises the maximum every once in a while. It arrives to minus 100 (more or less) activities placed in a few seconds, then it arrives to minus 30 in about 30 min and minus 20 in 5 or 6 hours, during all the time the placed activities are between 2 and 5 less than the maximum and not changing quickly (sometimes they stay for hours).

I have built the data adding activities and trying timetables and it would colse in few seconds as long as I did not place the last 10 subjects that are "Educazione fisica" and "informatica", but when I added those activities I also added the time constraint for all students to begin early and to have min 5 hours per day (those constraints were impossible without completing the data....

I also tried to add the time constraint of early beginning for all students without having completed the activities and FET could not close the timetable after 17 hours...

I'm thinking about splitting some 2 hours activities into 1 hour activities with time constraint not at 100% but at 95% so that FET can decide when to put 2 hours one after the other, would this help?

If I put the minum days between subactivities to 1, what percentage should I put to let FET decide when putting 2 hours one after the other and when not, but without the possibility of having 3 hours in the same day?