3 hours would be right if I were doing it at home. 1 hour to change the solenoids and then 2 hours to clean up the huge mess of fluid everywhere!
It's about 15 bolts, and one gasket. Not exactly a hard job so if a shop is asking 3 hours book time it's a bit much. OEM Toyota solenoids work best but aftermarket ones work in a pinch. It's just a solenoid that takes a 12V signal so not exactly hard to duplicate.