Last year, the graduates had to arrive at 8 for a 9 am start. It was so backed up- cars were in line for 45 minutes to drop their kids off. Best advice is to not follow the big line of cars and go straight at the circle off the highway. Find any parking garage and just walk to the stadium. Also, before your graduate actually walks in (they have a separate entrance), pick a meeting place for after.
Other than that, it’s a fantastic venue for graduation, so just enjoy the day!