20 - 30 minutos
My iphone would shut off with about 30% battery time remaining and it got progressivly worse and would shut down at 50%. After searching forums I decided to change the battery.
It took me a little over an hour to complete the repair and not 15 to 30 min as some people stated and videos shown.
My only advice is to TAKE YOUR TIME as you will find out there are a lot of small and delicate components in your phone.
Just follow the instructions and you should have no problem changing the battery.
My phone lasts all day now with a full charge.