If you really want to get your guys in shape, take a 2 hour class and make it 1 !
Take your 3 min rounds with 1 min break and make them 3 x .30sec ( although 2 x .30 sec is probably more realistic)
Take your 20 min warm up and make it 10 BUT do all the stuff of the 20 min !
Now were cooking with gas !!