The ticket window is open before the park and the line is short. That's not a problem, parking garage is open at 8am, get there at this time. But, you must process your AP before leaving the park. At either one, you enter, and head to the left, to the processing center, where you fill out a form, they take your picture, and give you a card. If you are first to the gate, and enter the park, it will only take a few minutes, and you'll still be ahead of the crowd. This is the best idea. If you get there late, and the line is long, you can come back.
Last year at IOA, we did it in the afternoon, the line was about 20 people out the door, but the wait was only about 20 minutes, not bad. They usually have 4 people in there processing the APs.