20 - 30 Minuten
My 3GS wouldn't turn in or charge, anything. It just stopped working one day. So I read up why it did this on iFixit and saw that there was a chance the battery needed to be replaced.
Honestly I went to another site to buy a battery. Trying to save a lil money. That was a mistake. The company sent me the wrong battery twice. Company obviously did not know what the were doing. Just trying to sell something. So I finally went back to iFixit and ordered the right one. It came in fast and gave you everything you need to replace the battery.
My only advice is to stick with the pros. It only cost a few more bucks and it's right the first time. Thanks for everything.