The timing of port transfers is always based on demand. As most flights from the US land in Sydney first thing in the morning, Princess will have transportation waiting for you. No, you will not have to wait for hours. You might get a tour of Sydney so you arrive at the port close to when boarding begins. Immigration, claiming your bags and Customs might take an hour.
But why arrive day of sailing? First of all, it's risky. Given the length of the flight, there are crew rest restrictions that can cancel your flight pretty easily. Plus Sydney is a beautiful city...spend a couple of days seeing, getting over jet lag, and making sure your bags make it with you.