The only state that requires a change within a time frame is a territory, NT. The rest accept that you have paid rego for a particular period of time and allow you to change over at the end of that period of time. At least this is what I have been given, in writing, each time I have been moved interstate by my employer. if you take a look at the RMS website it'll tell you pretty much the same thing.
That said, in your case you will have to change it over as it is a change of rego from interstate, not simply moving interstate.
Hi Matt, can you direct me to where it says that on the RMS web site
I found this
Quote from RMS web site,
Interstate vehicles
You can drive a vehicle registered in another Australian state or territory in NSW. If you’re only temporarily in NSW, you don’t need to get NSW registration as long as your vehicle displays all the number plates and registration labels required by the interstate authority.
If your vehicle is no longer temporarily in NSW, you should apply for NSW registration.
Corporations must not cause, permit or allow such vehicles to be used in NSW unless:
The vehicle has been owned, controlled or managed by the corporation for less than 90 days
The vehicle was outside NSW for at least 48 hours in the last 90 days
The corporation is in the vehicle leasing or hiring business, and the vehicle was leased or hired to the same person for the last 90 days.
To me that reads that you've got 90 days to transfer and not until your interstate rego expires. unless your here temporarily.