You asked for it...
A penalty unit is currently $137.85 so the
maximum penalty under s362D would be $13,785 or 6 months jail. All the jurisdictions have dire penalties like this.
Unusually, Qld have published the
new border direction (No 56!!) in advance of Monday. I don't think there would be any prosecutions for failure to get a day 5 test where you intended to but were unable to. Here's the primary requirement for domestic travellers from NSW or Vic or Adelaide
"Will undertake a test" means you have to arrive with the intention of taking a test. I can't actually find a requirement to take the test itself in the declaration that if breached would give rise to potential penalty. The day 4 or 6 thing that has been bandied about is illustrative examples of "as soon as practical". In the circumstances you mention it doesn't look like it would be practical to get the test until after you have returned to NSW, and once there it looks to me like you would have a reasonable excuse - you're back in the hotspot.
Cheers skip