The journey on the boat takes minimum 14 days from japan to an Australian port. Ships from japan doesn't leave everyday and there is always a long queue of cars waiting for their turn to get on a ship. After the car arrives, it will go through quarrantine and check for soil underneath the car. If soil is detected, the car will be washed thoroughly ( charged in to your account ) and this will delay it even more.
A customs agent will then take over and settle all the paper work including cost of freight, import duty, etc. This alone will take probably a few days.
Compliancing all depends on how modded the car is, if it is stock then no problems it will go through in about 7 working days. If there are problems, it'll take about 2 weeks or so.