If lessons are regularly running over I can understand sisters getting annoyed it frustrates me as it has a knock on effect regardless of if you have RS first or last. But there are steps you take to prevent that happening - for example you could have a clock at the back of the room where the teacher can see or you could make yo cards that someone sitting in the front can hold up saying 10mins to go, 5 mins to go and either 2 mins to go or finish up. While I didn't like it for me as I don't over run it has been used effectively in our beanch in the past