We actually take 20 minutes for Free Friday. If students had days where they neglected to do homework or didn't get their agenda signed they have to sit out the first 15 minutes of Free Friday. We rarely have anyone sit out. Bonus: parents are signing agendas each day and staying informed about their child's work and homework is being completed.
I do have a couple rules though. Kids have to be caught up on their work. They have to first catch up before they can play. They also have to have a clean desk. For those who can't quite figure out how to keep their desk clean all week, they at least get it clean on Friday. I believe that is important so that kids can stay organized.
During Free Friday some kids choose to do their homework.
Some choose to play with electronics.