In my experience, these timed take-home exams always gave me more than enough time to finish the exam to my satisfaction. So I'd say if you need more than 8 hours, you're just stupid, and no matter how much time you take, you'll do poorly on the exam.

A desire to work with others would also suggests that you are stupid, for two reasons. First, why give your peers the advantage of using your answers? Unless you're stupider than they, working together wouldn't benefit you. Two, you'll get caught very easily doing this, and get kicked out of school.

Finally, cheating in grad school is pointless; you'll get good marks even if you turn in a piece of dog sh!t.

Unless you're truly posting this question out of curiosity, you are a fool.