Just to reiterate, it is POSSIBLE but completely unknown whether a room will be ready early. Disney resort hotels average 90% occupancy. That means, on any given day, hotels have dozens of rooms vacant from the night before to accommodate early arrivals. Plus whatever rooms are cleaned at the start of the day.
DVC resorts operate at virtually 100% occupancy. Meaning rooms aren't available to new guests until they have been vacated and cleaned. And the departing guests have until 11am to leave.
If you stay at a DVC resort, you absolutely, positively must plan as if you will not have access to a room until 4-5pm. If you have an urgent need for access 6 hours early (child nap?), make different arrangements. Yes there are people who have gotten a room by 11am. In the grand scheme of things, it's quite rare. Over 20 years, I can think of one example where we got our room that early. And it was a slow season at a slow resort where the room happened to be left over from the previous night.
My own personal average is probably around 2-3pm and there are many times it has approached the 4pm deadline.