2 - 5 minutos
I shattered the rear panel of my iPhone 4 last week. I ordered a transparent rear panel from Ifixit and before it arrived, my 2 year old daughter threw the phone across the kitchen. The front panel shattered. My brother had a spare front panel that he'd got for free from a buddy at Apple.
I used one of the guides from ifixit and was able to successfully replace both screens in one hour's time.
Don't look anyplace else for guidance. I can't think of why anyone should look anywhere else.