1 - 3 heures
I had an iphone4 that I had kept after I upgraded so that I could use it as a testing device while I'm at work (Im a digital producer). The screen and back panel had been cracked from getting out of the car a little too fast and it dropping on the pavement.
After getting quotes for $100 to fix a phone I'm only going to use to test websites on, I figured I'd give fixing it myself a try.
At first I was naive in thinking this would be a pretty quick fix. Unfortunately, Apply designed these so that it's pretty tedious to switch out the display. Following the guide on this site, and with good lighting, some wine, and about an hour+ of time, I was able to switch out the displays.
I followed all of the slides in reverse to put the screen back in and it was no issue at all. It powered on, and now I have a new display.
If you don't have a magnetic pad, like me, take a sheet of paper out and fold all the edges about 1cm in, making a pan-shape. With each screw and each piece you remove, document it on the sheet and leave the piece on the paper - circled or specified as the part it is.
There are so many different mm screws that you will want to document every piece and where it came from so that there are less questions as you put it back together. And make sure you have good lighting!