Here's how DVC villas end up being available for cash reservations:
1) Disney retains ownership of a small (<10%) percentage of the inventory in each DVC resort. These can be used for anything Disney wants - hold 'em in case a villa needs to swapped out for maintenance, upgrade customers from other overbooked resorts, etc. Ultimately, I'm sure most end up with CRO to be booked for cash. Now, if a resort has not been completely sold to members (such as AKV or BLT), Disney's ownership percentage will be higher, so you'll see more of those villas available through CRO. I've heard that at least some of these get deposited with CRO at about 10 months out, but I''m sure it varies.
2) When members exchange out of the DVC system to use their points for cruises, stays at non-DVC resorts, etc, a villa of 'comparable value' gets taken out of the member inventory and sent over to CRO to be booked. The proceeds of that go to pay the other resort or the cruise line. DVC members tend not to trade out a lot, though, so there won't be a lot released to CRO for this reason.
3) If a villa from the member inventory is still not booked by 60 days out, it gets sent to CRO and put up for cash reservations. This is called breakage inventory. In this case, if a member calls looking for a villa like that one, it will be pulled out of the cash inventory and back into the member inventory.
So....the bottom line is, at resorts that are sold out, there are not going to be loads of villas sitting in CRO's inventory, and except for the breakage inventory villas that get moved over at 60 days out, there's no set time that they'll become available to the general public.
I wish I could give you a timeframe, but really, the only thing you can do is keep looking.