I don’t consider using frequent flyer points for domestic flight upgrades as I can put up with an economy seat for 4 hours.
Long haul is a different matter and I have upgraded several times.
When Do You Get Upgraded?
Your request will only be processed in the day or two prior prior to the flight as they are hoping that there will be a late full fare booking to fill any vacant seats.
Often I have only found out I have been approved at check in.
Often there are more people wanting an upgrade with points than there are seats available.
Qantas along with every other airline gives first opportunity to higher status members.
So its first chance to Chairman’s Lounge members ; followed by Platinum One members, Platinum members, Gold members, then Silver and finally Bronze.
It is not really clear; but I believe that your fare class can influence your chances, with a budget fare booked months in advance being less likely to be allowed to upgraded than an expensive fare booked within a short time of the flight..
I’ve also found its often easier to get an upgrade for a single cabin level improvement so going from Economy to Premium Economy is easier than going from Economy to Business.