being able to work on it over a couple days often ensures that the job gets done right... often times there are little things that come up that are unforseen, and not feeling rushed to get something completed that day often helps to make sure you get everything done perfect.
heck, just getting the flywheel properly machined can take a good few hours, and it's the last thing to come off and the first thing to go back on... and you want to be sure the flywheel is machined properly. most clutch shops don't have the proper machine, so the flywheel has to be dropped off... and often the sign of a good machine shop is having to WAIT for the work to be done! LOL!
figure you drop the truck off at 8-9AM, they're gonna want to let it cool down a little... figure it'll be torn down by lunch hopefully... flywheel gets dropped off and if it's put on a rush, they might have it back in a couple hours (assuming the machinist didn't slack off for lunch like mine all do!) figure the flywheel is back at the shop by 2-3PM... putting the truck back together can easily put you very close to closing time... and that's assuming that NOTHING goes wrong (which as we know usually isn't the case)
and they have multiple other vehicles they're working on at any given time... and they're not going to run to and from the machine shop multiple times a day... generally once or twice a day...
just because you find a shop who'll tell you, "sure, we can have it in and out in a day" DOES NOT MEAN that they'll actually DO IT!!! I don't doubt that they'll try...
I can probably guarantee you that anyone who's straight forward enough to admit that they'd prefer to have it for a couple days could probably actually pull it off in a day, and if you made your desires known and offered to pay extra to have your "priority level" raised, it could probably happen.
now, if you've got someone like SBC or someone else who specializes in this stuff, they'll generally have good machined flywheels on hand or the machines to cut the flywheels, and you instantly save a few hours... definately enough to make the difference between a 1 day and 2 day job.
Forrest