How long does it take to fix an iPhone 4 screen?

My nephew cracked my screen and I'm taking it in to a local store tomorrow to get it fixed. How long should it take for him to replace the screen? The guy said he'd fix the front and the back, though the back isn't cracked. He isn't charging extra for the back, though, so I don't care.

It should take a max of two hours for Apple to replace an iPhone 4 screen. It's a pretty quick process as long as the store isn't too busy.