2 - 3 hours
On my iphone 5 Siri stopped working due to a faulty rear microphone and my wife's lock button on her 4S failed which caused her annoyance.
My iPhone 5 was quite simple to repair. I wasn't looking forward to her 4S since that was far more involved. That said, the guide was very helpful and everything went just fine. We are both very happy to have full functionality again.
Take your time and never press really hard.
iPhone 4S Power and Sensor Cable
iPhone 5 Front Camera and Sensor Cable
P2 Pentalobe Screwdriver iPhone