[theFONZ]

If a mechanic finishes a "2hr" job in 1 1/2 hours or 3 hours, he still gets paid for 2 hours. If it takes him less time, he makes more money because he can start the next one early. So the incentive is not to meet book time but to beat it. After experience, and as new tools and techniques are invented, the estimated time is lowered (or raised if the job sucks more). The time the book says is from your car pulling in to out and all tools/equipment is cleaned and stored, not the time it takes to change the part.

It's not a perfect system by any means, but it's the one most use. If you don't like/trust that system, work on your own car.