10 - 30 minutes
Battery stopped holding a charge.
Pretty easy - battery and tools seemed to be of good quality. The Mac now will hold a charge.
Be very careful not to strip the screw heads... and be ready to clean out a lot of dust from the fan and other areas inside the case.
MacBook Air 11" (Late 2010) Replacement Battery
P5 Pentalobe Screwdriver Retina MacBook Pro and Air
Nylon Tipped Tweezers