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When you apply for a Transit (subclass 771) visa, you will be required to provide confirmation of your inbound and outbound flights. These are the only documentary evidence where the visa officer can work out for how long you will be in Australia.
Given these documents would show that the gap between arrival and departure is more than 72 hours, it will be difficult to satisfy the officer that you "intend to remain in Australia no longer than 72 hours" (clause 771.211 of Schedule 2 to the Migration Regulations 1994) for the visa to be approved.
You may wish to consider either changing your itinerary, or apply for a Visitor (subclass 600) visa instead.