POS SOFTWARE
If you are going to to use Australia Post as a delivery agent if you require your goods to arrive by Christmas, then you better send it now. Even with Express post would be the latest you could send it. When I rang up on behalf of my clients, I was told the bushfires would not be an issue, and then they referred me to their calculator.
Of course, the claimed delivery schedules and actual arrivals do not always agree.
I would suggest that you set our software delivery options to reflect this.