The sale starts at 12:01am on the 15th, however it may go live a bit earlier. Found the code via Cashrewards, so this means you will also be eligible for
5% 10% cashback on all purchases using this code.
Update 12:16am 15/12: The CR link appears to be active, however the code is still not being accepted during the checkout. Changing start time to 9am today. If it's not active by then, I'll get this post removed. Sorry for any inconvenience
Update 12:25am 15/12: Apologies to everyone who couldn't get the promo code working, the code is actually EXTRA25_AU, have updated the post. Thanks Lexington