You have to dump everything you know about requirements and what you've already designed into designing the next class, and then pick all those bits up, and do it again. The first class of the day is okay. The second is a bit worse. By the time 1600 comes around you can't see properly and things are fazing in and out of focus.
Time to go home methinks.
Acme points out that 1600 is unclear. I mean 4:00 PM rather than 1600 classes.