What samantha said, about 15-20 minutes.
These are the songs she is singing there.

B-Stage

And while "Say my name" she runs back to the main stage.

I would recommend the seats in front of the stage. I don't how expensive they are in the US though.
I had those and they were pretty good. But I also had the luck to get VIP. A woman ran into me and was like, "hey,you want to go VIP?" ..of course I was like "YES.image" image