I'd suggest a matter of days, 5 at most... But of course, no crystal ball!
That NOPTA website shows other (completed) applications, I tried to find similar (Extension on Exploration Permits, in VIC), but there weren't any recent ones still available to view...
But you can find many in WA. Looking through these, NOPTA were giving approval in ~1 to 3 days timeframe ("NOPTA for decision/implementation" being the status of VIC/P47)
Here's a couple of random WA applications (within the parameters they I mention above).... 1-3 days at this "NOPTA" status.
