In my experience, if there are seats (possibly at least 3 based on other reports on this forum) available, they will process the upgrade ~2-3h before departure at check-in. I think I have 100% success in upgrading with Qcredits/Avios at check-in between Europe and Doha when I asked, and probably 40-50% success between Doha and Australia. So the upgrades are not guaranteed, but depending on loads you can have a good chance. FWIW, I don't know if status matters to release the upgrade with seats available, the check-in/lounge attendant usually first checks loads, and if it looks good, they call someone to request authorization and I regularly hear that they mention status of the customer.