During the peak festival times the shuttles are running every 15 minutes so when you see the bus come to drop people off at the campsite you start to walk back up while the bus turns around. Normally that is the perfect amount of time to switch gear and down a few cold ones. You can certainly make the turn without missing more than one set, with proper timing you can make it back for the end of the set.
It is only 7 miles to the campsite, so maybe 15-20 minutes one way. The long wait comes when you have to wait forever in line to get on the bus (Lots of bus stops though
), or if you don't time the busses right on the way back.