I don't know if this is still the case, but when I went two years ago, you could stay in Diagon Alley past 5 p.m. (the Studios official closing time). If you had a park to park pass, you got a wrist band allowing you to stay until (I think) 6 p.m. But to leave you HAD TO take the Hogwarts Express, which did have a pretty substantial wait. We were only staying for one day so we were happy to have the extra time.