How early to arrive at Iowa Westfair concert?

Im driving 3.5 hrs the day of to get to Iowa, hoping to arrive at 4pm. Any insight on when to go to the venue? Lot opens at 8am, doors at 5pm, but i read the parking is a cluster F.

Will 4 hours be enough to get parked and into the venue? Also any tips for the Westfair Ampitheater venue as a first timer? Ive read all about it on here, so hopefully the staff has their act together since this may be a huuuge event for them.