There is a two hours long (double) math lesson, and we do not want it to happen on Friday. How to do it?

You can enter a separate subject “Math_2h” and prohibit it from going on Fridays.

Another option with additional relationships: choose “Max. number of periods per day “, enter 1 period, select the required classes / teachers / subject, and mark Friday.

Since double lesson takes two periods, this condition will not allow double Math lesson to occur on Friday.