I can do the front brakes in about one hour for both.(you might want to give it a try). Generally if you can easily push the pistons back into the calipers, the calipers should be ok......If brand new rotors are warping, that can only be because the rotors are getting extremely hot....this would happen if your calipers are sticking, but I can't think of much else that would cause that kind of heat. Sometimes one type of pad will fit in the slots of a caliper and still be the wrong ones. I wonder if your shop is using the right pads. "Crunching" is a strange description for warping. Normally with warped rotors you get pulsing in the brake pedal. Ask your mechanic what torque he is using on the lug nuts.....