2 - 5 Minuten
After 2 years without a case, my iPhone 4 finally had it's a$$ handed to it by a porcelain tile floor. The front display shattered and I decided to fix myself. Since it was coming apart I decided to replace the battery and rear glass to get it back to 'new' again.
Took 1.5 hours but it went back together nice and clean. Unfortunately the camera wouldn't work (frozen on shutter) after but that seemed to be the only problem. I then realized if it was in sleep for more than 2 mins it crashed and powered down. The only way to revive it was a home/sleep button reset. I took the camera out, re-installed and that resolved all issues. Back to 100% now!
Make sure the camera goes back in exactly the way it came out. Not sure how or why it didn't work the first time but clearly something was off.