Apples predominately is 10 - 14 days, but as all things agriculture depends on the sun. I've had years as short as 5 days, and some that last 30, but the majority of the time 10-14 is the normal.
Also judging the length isn't hard either I can normally predict when the bloom will be over as good as the grower just by watching the forecast and keeping track of temperatures. And I talk with my growers 2/week keeping track of their bloom progress. Don't wait for them to call you, you call them and the scheduling will be a lot smoother.
Find out at what percentage of petal drop does the grower release? If they hold out till 100% petal drop then that can prolong the amount of time the bees set there. However most growers can't wait that long to get the petal drop spray on so they normally call you around 85% petal drop to schedule removal in hopes they are gone by the time they hit 90 -95% petal drop.
Also the variety of apples they are growing will make a difference.
As for price I do apple pollination on a rather large scale and I charge $55/hive(including Virginia). I base my price more off of how hard the spreading is. If they want one pallet every 100 yards it is more moving for me. If they allow me to put groups of pallets down in one spot I give them discounts. I have a few growers who unload the truck and spread all of the hives with their own tractors, I give them an even bigger discount.
Something else to ask your grower is if he has wagons. I place quite a few pallets of bees on wagons at one central location and the grower will then have them pulled to where he wants them placed for the duration of the pollination. The egress works in reverse, bringing the wagons all back to one central location to load them back up.
