Reservations (Timing for Nitely Res System Purging)

[kcb1dizbksfan]

I am trying to book a Disney trip for a few days in early October (10/5) and all the resorts show sold-out . . . the first time I ever encountered this problem in 30 years . . . especially during their "off-season".
Does anyone know the best time to check on-line of call for cancellations when the system is purged of reservations that are not paid for or other factors that would cause someones reservations to cancel and be placed back in the availability status.