Free time in your regiment usually comes before a week of service or duty. This means getting your guard uniform ready, your operational back pack ready, getting your hair cut and getting your locker sorted out in case there is a spot revue.
It can come after time on terrain (in the field) which means cleaning all your kit for the next outing or course.
Overseas, if you are not allowed out because it's just a four month stint and the nights allowed into town are rare, then you go to the foyer, or buy beers and sit outside your tent or hut with your mates and drink beer.
Or there might a cinema that you can go to. Then it's down to reading books and talking with your mates until lights out. But no matter what way you spend it, you will appreciate it because it's in short supply in the legion.