You should try to get there an hour earlier, which is when the doors open. If you get lucky, or if the guards are in the mood, you can go down their and try to ask the guards to get autographs, and they might say yes. Good luck.
If you are a season ticket holder, you can get in 2 hours ahead, but only as far as the outer perimeters of the venue. The inner stanchions aren't taken down until 1 hour prior to tipoff.
It depends on who's playing and where as to getting autographs. Some teams have thuggier fans than others so that security may prevent pre-game autographs.