My experience has been that more V class seats become available at the 72 hour mark. If I book my ticket and waitlist, I can usually go to delta.com at the 72 hour mark and find my itinerary says 'Contact Delta'. I've had seats clear at the 24 hour mark too. I think depending on the route, Delta may open seats for the different medallion levels at those time windows. Of course, I've sweated it out at the gate too, only to find the bording card reader printing me a new seat assignment