I went that weekend probably 10 years ago now. At that point, most of the day wasn't bad. "Most" groups seem to buy tickets only to the concerts. So USF can start getting busier about 4:00. IOA was a little bit busier on Saturday with people who bought packages. But, it's still September and extremely low crowds.
If you haven't bought tickets yet and aren't planning on getting A/P, The Rock Your Weekend Package with tickets to the concerts and park tickets for Thursday Friday and Saturday are cheaper than 3 day tickets.
I've read horror stories about RTU (and NOJ) crowds but I didn't experience it the 2 times I went. I also stayed around the concert areas during the concerts. Other areas of USF during concert hours might be where the problems are just because you have a large group of lightly supervised teens and tweens and many churches use this event as an outreach. But, like I said, I never experienced it and the one day was a complete downpour and bands were being postponed left and right and rides were being closed. But the youth around where I was were as good as could be expected.