It’s not illogical at all. QANTAS uses an airline booking system used globally and the default timezone for many computer systems is UTC.
Setting up a promo to use AEDT would take a little extra work. Maybe QF now does that, but if they haven’t and it still runs on UTC then bookings made just after the end of the promo dates might get DSC, but I would never risk it and you wouldn’t have a leg to stand on challenging not getting DSC for such a booking.
Whilst I do have WP, I would prefer not to have to chase missing DSCs so I like to book after midnight UTC on the opening day of the promo and also avoid booking too close to the end of the promo as well.
The words in the Ts&Cs always state AU time, it has always been like this be it DSC, double points or any other offer. The booking engine works in UTC and it has always been like this. It is the way the booking engines work and local time zone is just configuration, hotel systems work the same.
To your second point, you can actually book flights past midnight on the last day so depending on your time zone and in this case you could book until around 11am SYD/ MEL time on 19 Mar and DSC would still apply. I have tested this theory in during previous DSC and other offers and it worked.
A question for both of you: Do you understand how timezones work?
Do you think that Qantas, an international airline, does not understand how timezones work? Are you seriously suggesting that Sabre, Amadeus and the other one have developed these systems used by 100s of airlines and they do not understand how time zones work?
It is illogical.
They set up the promo based on East coat time - might be AEDT or might be AEST. Right at the moment midnight in Sydney is 13:00 UTC the day before. Midnight AEDT is 13:00 UTC!
midnight UTC would be 11:00 AEDT. If they set it up on midnight AEDT they are not setting it to 11 hours after the promo starts.
@Matt_01 you claim you've booked 11 hours after and got DSC. Maybe on the last one - i haven't checked if I got DSC for a booking at 00:02. But otherwise, not my experience over 15+ years of DSC promos.
Edit: as platinum I've never really found contacting Qantas about this stuff to be painful. YMMV