Professor for a performance class is scheduling class time different than the class time listed in the catalog
Performance groups, even when taken for credit, operate outside the "norms" of scheduling. It is unlikely that your concert will take place at the same time as your scheduled rehearsals, so you will need to make an "exception" to the rules just to participate in the performance—which is kind of the point of the class in the first place!

That said, the faculty member overseeing a performance class does need to be respectful of the schedule to the greatest extent possible. It is not fair to ask students to completely rearrange their schedules when alternatives are possible. If the faculty member does not believe there are enough scheduled hours to get things done, then there needs to be an adjustment in the course.

However, he will "get away" with this unless people make an issue of this. It sounds like there are a large number of people impacted. If so, then there is enough ground support that you can challenge it collectively without reprisal. (You can also "take it up the food chain" if the professor is unwilling to make changes.)