What was happening at MEL last night?
Early evening flight from ADL > MEL Weds.14th, DEP delayed for an hour, PA announcement "due flight restrictions in Melbourne".
Later, on board announcement from seat 1A "MEL ATC have imposed a 90 minute delay on all flights, and no-one I've spoken to can explain why ...".
If WX holding or something else, one would assume it would be apparent from forecast/TTF or NOTAM.