10 - 15 minutes
I had two issues.
First my battery was bad (confirmed at the Apple Store). My iPhone 5 would randomly shut off between 20 and 60 percent and I couldn't get through a whole day on a charge.
Second my lock button would only work if I pushed on it really hard on the very left side.
The battery repair would have been pretty easy but getting the audio control and power button cable out was a huge pain. You have to take almost every single connector and screw out! While I was taking everything out I thought there was no way it was going to come back together but when I got to the end and started to reassemble it was actually pretty quick. I used the magnetic mat to write each step and then draw little circles labeled with the screw sizes so that kept everything really organized.
BE CAREFUL WITH THE BATTERY! I figured I was replacing it anyway so I started prying it out with a screw driver. I barely got the screw driver under the battery and flames started literally jetting out! The casing of the battery is extremely thin so be careful like it says in the instructions. Luckily it didn't melt anything important.