It runs 2:20...regardless of curtain. However: all shows seem to start 5 minutes late. So it will be over by 9. How long stage door "is" is up to you and how long you want to wait. It's impossible to know how many people will come out - but are you planning attending the closing performance? That will likely be a mess, with tons of people NOT at the show showing up for stage door. (And possibly add a little extra time - extra applause, possible curtain call speeches - but it won't add a lot.)
If we're not having fun, then why are we doing it?
These are DISCUSSION boards, not mutual admiration boards. Discussion only occurs when we are willing to hear what others are thinking, regardless of whether it is alignment to our own thoughts.