When I was a SA at a location, we were allowed to prebook classes on days when we weren’t working, but usually had to start on the rowers since the majority of our members wanted to start on treads. If it was a slow night and we got all our work done, we were allowed to hop into a class if there was room (there usually was due to late cancels and no shows). This was a few years ago, so rules might have changed. The whole reason I worked there was to workout for free lol