If the music is good I don't mind staying in the saddle for the whole class. I ride a tandem so I spend a lot of time in the saddle when I'm outside and don't get to wiggle. Most of the women in my classes seem very relieved to get out of the saddle on endurance days. An hour is a long time for people who are not bicyclists.
So what are the benefits of jumps? I stopped doing them because it's not a movement I can replicate on a tandem and usually do a seated sprint when the class does jumps.
Thanks,
Veronica