20 minutes - 1 hour
I had dropped a single drop of water into the crack between my computer chassis and the trackpad, this has been the second time (the first time I got Apple to repair it as a "defective" trackpad but the second time I brought it in, they said that the change in performance was not enough to constitute a replacement) and the clicking mechanism and clicking and dragging required excessive pressure to ensure proper function. So time for my own replacement!
The replacement was easy and took about 20 minutes. The toughest part was getting the ribbon cable through the weird guillotine structure and onto the logic board. Also, centering the trackpad was not as intuitive as it had seemed.
Plenty of light, and some needle tipped tweezers should be added to recommended tools.
Phillips #00 Screwdriver
Tri-point Y1 Screwdriver
MacBook Pro 13" Unibody (Mid 2009-Mid 2012) Trackpad