Australia Post have issued last dates for post to reach customers as below for parcels.
If you live in the following orders must be placed by these dates
NSW December 20th
Queensland December 20th
ACT December 20th
Victoria DEcember 20th
South Australia December 20th
Western Australia December 18th
Tasmania December 19th
Northern Territory December 16th
In all honesty i would give it a few extra days as being the silly season things are bound to get caught up and i DO NOT guarantee that goods will be there in time
This does not include envelopes which can take 2-3 weeks although i put priority stickers on every one to help speed things up.