45 minutes - 2 hours
Spilled water on the keyboard and the right half of the keys stopped working. Asked around for someone to do the repair, but Apple said they would erase my data and charge me an arm and a leg. 3rd parties were also giving me 500 dollar estimates.
Very easy and not difficult at all. Excellent instructions and iFixit sent me all the tools I needed to do the job... except for the phillips head to remove the trackpad which I already had. Would have been frustrating if I didn't.
Take it slow, read all the instructions. Also have plenty of space to line up all the screws you take out. Keep very close attention to the screws, and store them in the configuration in which you took them out. Some screws are longer than others. Be patient.
TR8 Torx Security Screwdriver
T5 Torx Screwdriver
P5 Pentalobe Screwdriver Retina MacBook Pro and Air
MacBook Air 13" (Mid 2012) Upper Case with Keyboard