I modularize my in-class assignments based on subjects covered. If a class runs long and we aren't able to cover a subject, I can push it to next week and simply push that module from the current assignment to the one coming up next week. This works really well because it means that I can adjust the length of my modules across sessions. In other words, if I don't want to shorten this week's lesson, I don't have to, because I can make changes to next week's lesson. This is also easier because I can give some thought to next week's lesson outside of the classroom, which means the adjustment will be better (or at least better-planned).