You have no legal obligation to divert at 2330 to B. Do you stay or do you go at 2330?
I hope that is a rhetorical question. Had you decided to "stay" in Canberra on Tuesday , which was also fogged in (same day as Mildura &ADL BTW) you would have found yourself severely out of luck. It was FC to clear at 0000 and did not actually clear until about 0115. You would be a mug to hang your hat on a forecast in the circumstances you describe.