2 - 5 Minuten
I dropped my iPhone on the road and rear glass with the lense was broken when I got off my car. I first contacted local phone shop, saw them my broken iPhone and their suggestion was just purchasing new iPhone. Unfortunately (or fortunately at last) there were no stocks of iPhone 4 on the shop and I was told to wait until new stocks will be coming. Then I went to rather bigger electricity shop and the salesmen gave me the advice that I do not need to purchase whole iPhone but just purchase rear glass because he had the same experiences. Actually I was about to purchase 600 euro's new iPhone but thanks to iFixit, my iPhone was repaired just less than 120 dollars.
Less than 2 minutes, very easy
should provide the necessity of screwdriver