On each of the other exams, the teacher had a rule "Once the first student leaves, nobody else can come in" because she let people take home the exams themselves.
For the final, she didn't let folk take home the exams, and instead kept them (and a sheet that says "I hereby confirm that this is not cheated upon). So I could go in and do the exam during the proper time, rather than just get shafted by the previous rule.
So I managed to get a high C on all my exams now.