It probably depends on the resort and how busy they are at the time, and how specific your requests are. On our trip last month to OKW, we arrived and checked in about 8:30am. We had been assigned to a building on Miller's Road. I had not made a specific requests with MS NOT to be there, but I asked the CM if there was a possibility of being anywhere else in the resort. He asked what areas we preferred and I said, optimally, Peninsular Road, Turtle Pond or South Point - any would be fine.
He offered us the "New" Bldgs on the edge of Miller's Rd. or Turtle Pond....of course, even if we'd stayed with the original assignment, the room would not have been ready until 4pm.
Anyway, we chose Turtle Pond and were perfectly happy there.
If your requests are general, and if the resort has a little leeway to move you around, you can sometimes get lucky at check-in. Just be sure to ask prior to your room cards being issued, and if you don't get exactly what you want realize there is probably a legitimate reason you could not be moved. The logistics of granting requests has got to be one big headache.