I found these 2 reports from the F! Thread.
It takes A LOT of folks to max out 2 shows-around 20,000.
We went to the 9:30pm show on 11/4 and got to Sunset Blvd around 8:30pm. There was a bit of delay getting everyone into the ampitheater after the 1st show (I think the show started 10-15 mins late) so we were probably standing in the crush of people for at least 45-60 mins which was pretty brutal after a full day at DHS. We got great seats right in the middle (maybe 5th row), but I don't think the theater even filled all the way, so we could have probably showed up right at 9:30pm and still got a seat on one of the end sections. Good luck if you go!
My daughter works at HS, she went last night and got in line at 9:00 and walked in for the 9:30 show without a problem. Hoping the mad rush was just for the first night.
We saw it with her during a cast preview nd it was awesome!