15 minutes - 1 hour
My 18 month-old iPhone 5 battery was dying by mid-afternoon, so I figured it was time for a replacement.
The guide was very accurate, and it wasn't so hard to get the screen off using the single suction cup in the tool set. However, on reassembly the screen stayed dark after rebooting. Plugging in to power elicited an iOS 7 "power connect chime" repeating every couple of seconds, but no life from the screen.
I took it apart again, and, looking carefully, saw that I had ripped the ribbon cable to the LCD when popping off the screen the first time. So now I've ordered a replacement screen, making this a significantly more expensive repair. I've done lots of button replacements on iPhone 4's before, so I'm not completely unfamiliar with iPhone disassembly, but it's pretty easy to destroy the screen when the iPhone 5 first pops open. In retrospect, I should have bought an iSclack - $25 is a lot less than $100 for a new screen.