There is a difference between being careful and being inefficient. It is a bad idea to take an extra 30 minutes to do a simple lab when the entire class is waiting for your group's data but have classes to go to after the lab class. Of course, you might have an excuse for being inefficient if of course you are inept at performing third grade math to allow times to overlap. But isn't there some kind of math requirement for Biology majors?
It's times like these that call to mind the Wizard's First Rule. (Read the book by Terry Goodkind.)