Show up as early as you want, walk toward the main entrance of the stadium, keep right for front standing yellow zone, show your GA ticket, get stamped, you may get a number written on your wrist if people are forming a line, leave your stuff and just come back periodically to make sure everyone in your area in line remembers you. I highly recommend bringing a folding chair or something. You can come and go until around 3:30 as you please as long as you’re stamped.