20 - 30 minutos
My iPhone 3Gs had a low battery. Couldn´t not hold power for long time.
The repair took 3 times as long as I expected. First time you are very nervous and thinking, that you are breaking the phone.
But no ! do it slowly, take som brakes and keep doing it.
The first batteri from iFixit, did not work, so 5 days later I recieved a new one, and did the repair for the 2. time, only 34 minutes from beginning til finish.
Do it slowly, best when you are alone. It is tricky at some points, but if you don´t loose temper, it will be done.