5 - 30 minutos
My iphone 4 is 22 months old and battery life was 4 hours.
It went great. Took about 10 minutes.
Replacing the battery was easy given your great instructions. However, after replacing the battery the battery life was still only 4 hours. I googled the problem and after trying several things that were suggested by people having the same problem, it finally came down to deleting my email account and reloading it. Now my battery life is 4 to 5 days. YEY!