The only Flat rat shop guide I have ever seen was published in the early 90's by ATA Spear headed by Jeff Covel of Amzee Corp. Unfortunatly that guide dealt with upholstery projects prior to that time. It was however a very insite full guide, especially for the newer shops, for breaking down all the steps in the process and assigning a time for each. It also included a chart for logging all of the overhead expenses that are often forgotten to help establish minimum shop rate.
Sadly Trimmers are excellent at there craft, but as a whole we are terrible business men.

To answer your original Question, Time and past experience will be your guide. On larger jobs, I developed a Materials and Labor spreadsheet to breakdown every step of the process. ( and should use it more often on the smaller jobs) After 40+ years owning the business I sometimes still miss the mark.

Thanks for the reply Patrick,
We still miss the mark as well...getting too old myself.. 45 + years lol

I was trying to come up with some kind of general time guide.
Say ; remove and install a bucket seat : 1 hr remove + install cover 1 hr + whatever work and material