DS/DD are on a block schedule so each period is about 90 minutes every other day. That does make labs easier although in my day, we managed AP science courses with labs within 50-55 minutes. The trick is in the planning, including preparing ahead of time, getting started immediately, and some labs can go over into the next day.

The after school exams also discriminate against school bus riders who may not be able to get alternate transportation . . . I guess they know to not sign up for those AP history courses.