With the possible exception of the Beach Boys - seating for Eat to the Beat, as well as Flower Power, is absolutely never a problem.
Arrived last year for Lover Boy 10 minutes after show time, sat in about the sixth row, but could've been closer. (And didn't stay long.)
Length of show is typically 25 to 30 minutes, although on Friday night, Survivor went for 40 minutes.
Please, please don't waste a minute of your evening queuing for this. Even if the queue stretches well into Italy - it's an illusion. The people in that line won't fill a quarter of the theater.
We've been seeing every group at least once, usually more, every year for 10 years, so I do have some experience with this.