Been at a PM for 4 years, after coming over from an AM. Here is my advice:
With prep coverage, ABSOLUTELY treat it like an AM. You must set hard deadlines in the evening, and if you don't get the info, call them up on deadline. You have to treat it like you have an AM deadline, or else you will run into problems getting info. No one likes to be called at 7:30 a.m., and many of these people work and can't be reached.
At our paper we try to have the prep and local sports paginated before the night ios done. We are rarely in past 11 p.m. but on heavy nights to midnight.
If you are doing any type of writing, I say set personal deadlines.
The beauty of a PM is you can really write and think out your story. There isn't that robotic AM gamer play-by-play drone. That said, don't stay up to 3 a.m. writing a high school football gamer. If you need extra time, take it. If you want to write it after a beer at the bar, or watching the big game, fine. But I would think all your copy should be in before 3 a.m (if it is that late it better be a great story too). Writing on deadline at 8 a.m. is unacceptable.
And don't let your AM buddies give you crap. They have an excuse for their drivel (time). You on the other hand are held to a higher standard.