What Chris Herbst is telling you is the shop should not charge more than the flat rate for the job. Mechanics have flat rate manuals which tell them how many hours for specific mechanical repairs. Good mechanics can always beat the flat rate time, but there is that job that something goes wrong on... Jobs are usually priced off of the flat rate manual, but if you paid more than that, you paid too much, and probably paid for someone's learning how to do the job.

For what it is worth, as a shade tree mechanic I changed the broken timing belt on my wife's 1986 745T at a road side rest area in one hour and 12 minutes, start work to drive the car. I used a Coleman Lantern and a flashlight to see my work, and it was 40 degrees and raining. I had lots of incentive to do the job fast, and I had done it before.