Two things:
1. If you're talking about getting the size and class room that you reserved, that happens 99.999% of the time. Resort inventories are tracked meticulously.
DVC resorts do not overbook. If you booked a Two Bedroom Savanna-View villa, you will get that type of room.
There have been a few random reports lately of people not getting the room they booked. Almost all of these appear to be related to construction issues at AKV. By the end of this month all of the rooms scheduled to open this year will be open, so that should not be an issue.
Don't let those reports scare you off. The odds of not getting the room that was booked are miniscule.
2. Now if you're talking about getting
requests associated with the reservation, that's a different matter. The resorts will do their best to satisfy members' requested locations, floors and such, but there is absolutely no guarantee. I suspect the later you arrive, the less chance there will be of having requests met. But even getting to the front desk at 7am does not guarantee you will get your ideal room.