30 Minuten - 2 Stunden
I dropped my I4s 3 days after I got it and the camera wouldn't focus after that. I replaced the screen so I knew how to get into the 4s.
The repair went so fast and easily, I didn't bother to take photos.
I read where some people didn't bother to disconnect the battery. If there's ANY chance of zapping something, why not spend the minute or two to disconnect the battery?