We too are DVC members. They told us it was prior to checkin. Which sounds to me like 24hrs in advance. Just call member services and ask them.
By the way, DDP is well worth it. Even if you don't eat all the food... it's paid for in advance, tips included. From my understanding we get an even better discount being DVC members.
Good luck!
We are going Jan 28th - Feb 3rd.