The usual reason that a seller cannot close for such a long period of time is that they have a reservation at the resort that they intend to use. That raises the issue that you better make sure of the status of the points you are purchasing so that you will actually have points to be able to make a ressie for May-June 2014 because the seller may be using up points for the current or possibly even the next use year to make that reservation.
As to closing in late Dec, even it occurs then, you will still likely have two to three weeks thereafter before you can reserve. That will put you less than 5 months out when you attempt to reserve and your chances of finding anything at VWL for that late May to early June time of year that far beyond the 7 month reservation window are going to be low.
Also, unless something has changed, the seller cannot make a reservation for you that is going to occur after the closing. Disney cancels out such reservations at time of closing.