Officially Qantas allow bookings up to 353 days in advance, although if you're booking through a 3rd party that can sometimes be reduced down to 330 days which is more of an industry standard. The exact number of days (or at least, your perception of it!) can also vary slightly depending on timezones - Sydney is 10 or 11 hours ahead of the UK, thus it can already be "tomorrow" in Sydney when it's still "today" in the UK.
In the case of Avios, it looks like they allow the full 353 days. Currently the Qantas Australia website is allowing me to view flights up to December 25, 2013. The BA/Avios website allows me to select days up until December 26, but actually looking for the 26th shows no flights available on Qantas. Picking two typical routes (SYD-BNE and SYD-LAX) the availability appears to be exactly the same on both the Qantas and Avios websites for the 24th and the 25th of December, which matches what I've seen before when comparing the two.
As an aside, redeeming Avios points for most Qantas domestic flights is an excellent use of them - the redemption rates are far better than even Qantas Frequent Flyer points on the same flights!