In my 30 years...yes 30 years...of visiting SW I've NEVER arrived earlier than 20 minutes Bfor a show.....most times, 10 minutes.
I guess it depends on your definition of 'best seats' but I'd also note that most theaters are still roped off 1 hour b4 the show so.... In my experience the ropes drop no more than 15 minutes b4 any show.....but I may be off by 5 +/- on that.....
That said .... the pre-show at Clyde and Seymore is always a hoot for me...one I like 2 be sure I catch....
The show b4 the old ski show was good too....but by mentioning that, I show how long ago a first went to SW huh?