Who the heck knows is correct. The un-scientific background of seeing people post on the Dis that they did or didn't get requests, anecdotally suggests that requests aren't on any list ordered by the time requested. One would guess that the room assigners simply get the day's list of checkouts and previously open rooms, and then get the list of check-ins, and see how they match up.
But
DVC admin has never seen the need to make the room assignment process transparent. They do tell us that we drop to the bottom of the reservation waitlist if we modify our waitlist. Not so for room requests. Inferring that happens would simply be a guess.
The assigners do seem to pay closer attention to medically necessary notation requests, such as first floor in non-elevator buildings or closer to lobby, but even those are not guaranteed outside of a specific category (HA).
I am confident that the room assigner folks would prefer to make every guest happy. However when there are thirty studio check-ins at BWV on a given Saturday that have all requested "near elevator," and there are only ten studios coming available anywhere close to the elevators, then by definition they are going to not honor 2/3 of their requests that day. That's just how it works in a full-capacity timeshare.