In the end, someone has to actually get paid to squeeze the oranges or pick all the brown M&Ms out of the bag, but that cost is insignificant in the face of reassurance that the person with whom you are doing business is reliable and actually listens to you.
The crazy request may only be in there as reassurance that all the mundane details are being handled appropriately. If you screw up the barbershop quartet singing "Copacabana" to arriving guests while wearing Nicholas Cage masks and holding two quarters of a muskmelon apiece, with seeds, then you just might screw up the cake-cutting ceremony, too.
I know it's just an example but this actually seems like a pretty good illustration of the sort of thing that falls into the category of: We can do it. We can even give you a pretty good idea of exactly how we need to do it. But it's going to cost you a pretty big premium.
(And I'd add that high-end hotels probably routinely squeeze a lot of fresh juice for breakfast and have lots of staff doing various prep for breakfast starting in thee wee hours. It may not be a job I'd personally want but this isn't asking for some death march that's much different from day-to-day hotel operations. They may need to hire some extra staff and maybe rent some more juicers but there's nothing inherently difficult about this problem.
Instead buy a dozen automatic juicers and charge the client to buy new ones.
[1]The juice in an orange is highly variable by season, producer, ect. Just add it to the bill.
add some buffer oranges
Try to do all the squeezing within an hour, as buffer on time.
3000 oranges / 60 minutes = 50 oranges per minute to process
Using a standing orange press - chop orange in half. Put halve into press, push press down, open it up, pop orange out. repeat.
So perhaps 1 orange every 5 seconds. (Batch cut a bunch up initially). Approx 12 oranges a minute, lets say 10 oranges a minute for an employee.
So 5 employees can press 50 oranges a minute.
Add an extra employee as buffer.
So 3000 oranges, 1 hour, and 6 employees.
A particularly great example from fiction by the way is Heinlein's "We also walk dogs", which I highly recommend.
Going back to the original post, I might decide against taking the job after learning it was just a test, but that's a separate discussion.