As a guy whose program recommends five minute rest breaks between sets in the squat rack, I second the advice on hovering. It’s not at all rude to ask how many sets someone has left. When I get that question, I’ll typically offer to let that person work in. Failing that, it’s also the politest possible way to say, “I got next” on a particular rack… if you’re on record as wanting to use the rack, when I’m finished I’ll do my best to make sure nobody else grabs it if you’re still in the general vicinity.