I would not take the 11:30 flight as there are too many things that can factor into your delay in getting of the ship. We had a 12:30 flight and made it by the seat of our pants. Our ship was delayed by strong currents and didn't reach the dock on time. We were further delayed by the need for sniffer dogs to greet every passenger disembarking due to people taking food off at other ports along our route in spite of the Captain warning against this practice. So everyone and their hand luggage was inspected thoroughly before we could even claim our larger suitcases. Again,, going through the terminal and immigration was very slow and by the time we were through and into a taxi, we practically needed a change of underwear. By the time we got to the airport with some slow traffic along the way, we got to our gate and people were boarding. Too close for our comfort! Not worth the stress!
Enjoy Sydney for an extra day and be sure to eat at Pancakes on the Rocks.