Reward availability for short haul not much to do with load or how busy or not busy a flight. I've seen many examples that if on a day there are multiple flights to the same SH destination sometimes flights which almost sold out or significantly more expensive have reward availability other time I've seen the opposite. Obviously if BA does not sell any more cash tickets then no reward will be available too. Again in my experience the automatic process releases rewards seats around midnight or 1am UK time. Manual rev man reward releases usually UK morning hours. As others said there is no guarantee that BA will ever release any more seats for example. If the OP wants to travel on that day I would book the earlier flight with a Avios plus £1 cash and keep an eye on the later flight. If the later flight gets rewards seat availability then the OP can change / cancel whichever gives you the better deal. reward bookings are fully flexible until 24 hours before the flight.