That makes it much more interesting. I was wondering why the aircraft had so much fuel that it was able to return to Melbourne, and that Jeppesen plate pretty much explains it. My take is that it was not an oversight, but they were basically pushing the closure (as you might a curfew), in the hope that they’d make it, or get an extension. Looking at the positions and timing, they needed about 15 minutes, so not outlandish. You have no real choice but to launch, and hope it‘s sorted out whilst you’re flying. There wouldn’t have been any crew in Darwin, so a diversion there would have left them stranded.