If you have more time, take a walk across the bridge and have a good aerial view of the habour.

You could sign up for the half day climb of the Sydney Harbour Bridge and get certified.

There is also the Rock where you could have some refreshment while doing your shopping.

You could also take the ferry to the zoo or to the other side of the nude beach and take a bus back. Just take note of the timetable for the ferry as the last boat is at 5pm.