My wife and I are cruising around the Islands in Feb. First trip down under for both of us. Besides the port city points of call what might be a good 2-3 hour visit around the port cities?
Which cities in Australia? Sydney? Melbourne? Brisbane?
In Sydney, in 2-3 hours, you might like to visit the Centrepoint Tower (or whatever they call it these days). It's in the middle of Sydney City, and therefore only a few kilometres from where cruise ships berth. On a clear day you can see 30-40 kilometres, so you can at least see a lot of Sydney.
Alternatively, depending on your interests, there's the Australian National Maritime Museum in neighbouring Darling Harbour which has a few ships to visit, including tall ships (I think including the replica of Captain Cook's "Endeavour") and a former Royal Australian Navy submarine.
Or catch a ferry or river cat out to Manly (the part of Sydney adjacent to the northern side of the harbour entrance). It's a bit of a tourist trap but it's a nice part of town to just wander around in and get a good coffee from a street cafe.
Or walk around the Rocks, which is the part of Sydney between where the ship berths and the southern end of the Harbour Bridge. Again it's a bit of a tourist trap but it's also the oldest part of Sydney with some of the earliest remaining buildings.