Just visited 7/11/10. Actually stopped by the night before to know where the shop was for the next morning in case there was a line. The shop states that the showroom is open 9am-9pm. If you really wanted to pawn 24 hrs, they have a walk up window.
Visited early on 7/11 which was a Sunday. No line but none of the "stars" were there. The armed guard at the door with short hair was very friendly.
In terms of expectations, having watched the show regularly I expected that what you see on the show is about what the shop looks like. That 's basically what you see. The front of the store is the show is filmed, mostly at two counter areas and the front cash/transaction area. The rear of the store has some items from the show and a lot of souvenirs. You can't approach the transaction area unless you are conducting a transaction. Behind this counter is where everyone's desks are.
If you are looking for an experience to stand where the show is filmed and take some pictures you won't be disappointed. If you are looking to meet the stars and shake hands, you will need to invest time researching what items you have to sell and if it is "show worthy", are they filming when you are there and when the stars are present. You will then need to potentially stand in line outside the shop in potentially inclimate weather.