Because Australia is roughly the size of the contiguous United States, "enough" time depends on your scope. To see the "Golden Triangle" (Sydney, Uluru, and the Great Barrier Reef), 10 to 14 days is the recommended minimum. This allows for travel time between these distant hubs. If you wish to include the Great Ocean Road or Western Australia, you really need 3 to 4 weeks. For those on a tighter schedule, 7 days is enough for one major region, such as Sydney and its surrounding Blue Mountains, but you will spend a significant portion of your trip in transit if you try to visit multiple states in less than a week.