1 - 2 uren
Within one week, both my iPhone 4S and my mom's iPhone 4S had their screens shattered. Her iPhone's wifi and bluetooth already wasn't working way before that incident. I then bought two displays (a black one, part only, and a white one, with the fix kit) and an upper antenna. After making these purchases, I also found the repair guide for grayed out wifi on iPhone 4S, which I tried out.
The repairs went fairly smoothly aside from the fact that I forgot to put some screws back in place and had to reopen one of the iPhones after repairing it.
The only other problem I had was that I kind of folded and squeezed the new display's digitizer cable as I assembled the new display into the outer case, despite the guide's warning to pull the cables all the way through that slot. I did pay attention to that warning, but I thought I had already pulled the cables all the way through and was afraid to pull too hard and snap them. I only realized what i had done when I saw the digitizer cable would not reach its socket. The screen seems to be working just fine.
By the way, I installed the black display on the white iPhone and the white display on the black iPhone. Just thought it would look nice.
About the wifi/bluetooth, I replaced the upper antenna and also followed the "How to Fix iPhone 4S Wi-Fi Grayed Out" guide. I don't know which one of them actually solved the problem, I believe it was the reflowing procedure (wi-fi grayed out guide). I didn't have any kapton tape, so I tried using some thermoretractil tube around the board, which worked ok. Anyway, it seems to be working fine now, which is great.
Not very different from what's been said already. Be patient, keep track of the different kinds of screws and be careful when pulling the cables from the new display through the outer case.