How long are Katy Perry concerts?

I am going to a Katy Perry concert next Thursday, and I have a few
questions.

1) How long is the concert altogether (including the opening act)
2) On a scale of 1 to 10, how loud are Katy Perry concerts?

I have this problem where when I go to concerts, I always have to pee.
I don't know why, and I'm nervous that I'll have to go to the bathroom
in the middle of the concert and have to hold it for the whole thing.

The opening act is Marina and the Diamonds, I think.
Also, I think the concert starts at 7.