Originally Posted by LHR/MEL/Europe FF

Unfortunately it will be a problem.

TWOV runs from your scheduled arrival time to your scheduled departure time.

If your flights lands early - not a problem. But if your outbound flight is more than 72 hours you are outside the rules and you would be denied boarding at the point of origin.

being able to clear immigration on the outbound before 72 hours is not relevant, only the departure time.