45 minutes - 3 hours
My phone had gotten wet and the power button had started working sporadically, so I I replaced the button itself and the audio control and power button cable. While I was at it I figured Id replace the battery.
It went great. I replaced the parts and ended with a phone good as new. (http://instagram.com/p/pZ8lGjjNhG/)
Take it slow. Read everything, and keep everything exactly as you took.