Proposal

[miloudi]

One of the members of a proposal by making a feature or property of a / the minimum number of tasks in the time periods specified /

[Zsolt Udvari]

I think you can do it. See: http://lalescu.ro/liviu/fet/forum/index.php?topic=1197.msg6789#msg6789
My idea:
- create complementary of your desired time periods
- choose activities
- set "max number" to "activites number" minus "your desired minimum number"

[Liviu Lalescu]

Indeed, like Zsolt said, you can use negative Constraint activities occupy max time slots from selection.