I strongly doubt it. If the NT is anywhere in the equation, it adds an absurd amount of time.
3 months UK to Central Australia. Got to Australia and through customs under 3 weeks.
Post two registered post items at the same time to the same address, Central Australia to SE Victoria - one arrives in 3 weeks. The other arrives in 2 weeks,back at my address! Made it all the way to Melbourne and back, quickest I've seen, yet fiasco none the less. Took another week to leave the local post office and another 3 to get to the destination (correct one this time).
Order item from SE Victoria, travels from there to Sydney, Melbourne, Adelaide, Darwin before finally making it to Central Australia. To be fair, this trek only took 3 weeks.
Two instances where I personally witnessed the delivery driver stop and deposit the "sorry we missed you" collection slip in my letterbox without setting foot on my property. In fairness this was a couple of years ago.
One instance where I was receiving an item that by law must be delivered through a government licenced 'dealer' to ensure compliance with relevant legislation - I was given the tracking number of the item to the dealers address BUT online I was given the option to redirect the delivery !!!! I went through the process out of interest to the point where I had to confirm, then cancelled just in case the constabulary might take exception to my 'experiment'.
As a generalisation, I expect anything other than standard letters to take a minimum of 2 weeks and often upwards of 4. Overseas parcels (other than from China) typically take 3-4 times the amount of time once cleared from customs to get to Central Australia to what it took them to get from the US or UK to enter customs.
As others have suggested, directly or indirectly, keep track of stuff you are expecting - to the extent you can with Australia Post tracking
I figure the big boss of Australia Post on his unconscionable salary must be getting well paid for his efforts to privatise parcel delivery in Australia (by driving customers away from Australia Post ...). I feel a little sorry for the staff ... working for an organisation that has a bad reputation can be soul destroying ...
On a plus side - I now use a parcel locker and get notifications of mail in my PO Box via email. Parcel lockers have been great for me - email and sms notification that something is there, and avoiding the often 20+ deep queue at the collection window, I've only ever had to wait to use the parcel lockers once in many dozens of collections, and it was only one person ahead of me ...