50 minutes - 2 hours
My trackpad started randomly clicking, selecting everything, moving things around... very bad for a developer!
It was a cinch. 20 minutes tops.
Spend a little time with that last adjustment screw before putting everything back together so you don't have to open it all again.
T5 Torx Screwdriver
P5 Pentalobe Screwdriver Retina MacBook Pro and Air
MacBook Air 13" (Mid 2011) Trackpad