I looked through a Caterpillar Handbook and found data that will help the driver calculate how long it will take two 627F machines to move some dirt. We also have to learn beforehand how hard the soil is, how many rocks are there, how much the tractors sink into the dirt, the grade or slope they have to climb, the distance they have to move the dirt before dumping it, and so on.
Then, using the data provided in the handbook, you can determine how long it takes to move dirt. It appears from these charts that our pair of earth movers should take a couple (2-3) minutes per cycle of load-travel-unload-travel. There are lots of numbers here, but it's only elementary arithmetic, not rocket science. [click on the images to enlarge them]
If you can't calculate how much dirt can be moved per cycle, you'll never be able to give a quote to the customer who wants to have his area scraped. You might not have enough days in the schedule, your tractors may run out of fuel, or be unable to safely climb or descend a slope loaded with dirt, or the dirt may be too hard for maximum productivity, or too dusty for the local community to tolerate, etc.
I suspect this gets done well in advance by engineers in the contractor's offices, with only a little input from the drivers. Using the data in the chart and simple math enables us to make an estimate.
In our case, the dirt is fairly soft, yet the contractor has provided a whole fleet! The push-me, pull-you pair, a bulldozer with blade and forks to loosen the soil, a water truck to cut down the dust, a scraper to do precision earth-moving, and a roller to compact the soil once it's been moved. At least 6 pieces of equipment, operators, and fuel, water and maintenance.
Here's their assignment - take the extra soil (about 20 vertical feet, so we need to move 10 feet of depth) from the green area and move it to the red area. Level and compact the soil on the entire lot. Ready? Go!