EF is realtime. As others have pointed out in this thread, even on the day of Departure BA are often willing to sell full fare tickets in oversold cabins provided their systems are confident there is enough space further forward to OpUp into.
you'll often see something like F8 A7 J5 C0 D0 I0 for a ClubWorld Cabin that has no seats left to assign. Then in the minutes and hours before departure the FLY system will start OpUp-ing people as the system becomes increasingly confident it will need to create seats in CW for those with confirmed bookings but no seat