I had a 24-hour take-home civ pro final last semester and I did fairly well so I'll divulge my "pearls" of wisdom.
An outline is crucial - include case names and page numbers. Tab your casebook and your FR supplement. Next, study for it like it's closed book. Believe me, recall is much faster if you study like you would for a closed book exam. This is where the outline becomes really helpful. If the call of the question/instructions state that you need to cite to relevant authority, you can reference your outline to make sure you've cited correctly to every part.
Don't be afraid to take hour naps so leave yourself time for that. It's going to take you at least 24 hours to recover from the take-home. I'd also recommend taking the test at home if you live alone. Other students who take the test and stay at school will be really ramped up. You want to reduce the stress on yourself as much as possible.
I saved three hours at the end because I had 30 multiple choice questions on top of six essay questions.
Breathe and believe in yourself.