Obviously Qantas do not publish such information. However, in my experience, and resulting from my own research and discussions with many QF FF members, I understand the situation to be as follows:
When the flight is initially loaded into the reservations system, a set number of FF award seats are made available in each class. These are the X (economy), U (business class) and Z (first class) fare buckets.
Once these seats have been reserved by FF members (either QF members for awards or upgrades, or partner airline FF members for awards), they are no longer available.
If one of these reserved seats is released due to a cancelation or change to the original reservee's itinerary, the seat will be released back into the original X, U or Z bucket and become available for someone else to reserve. Obviously this situation can occur at any time.
The first time QF seem to review the loading and decide if more seats should be released into the award buckets seems to be about 2-3 weeks before the flight date. This can be seen from people having upgrade waitlists clear at about this time.
Further reviews seems to occur at 1 week and 3 days and the day before flight date. Again, these are the times that upgrade awards seem to clear.
However, remember that upgrades come from the same class buckets as awards for U and Z inventory. So anyone with a confirmed and paid economy or business class ticket waitlisted for an upgrade will get first look at any X or Z inventory that is released. Only if there are still U and Z available will they be left for people wanting to book award flights.
