How long is a piece of string? This is one of the things that can vary so much and is pretty much impossible to give you an exact prediction, how ever as a rough guide the best time to travel is as follows:
Non-Tropical Areas (South of: Rockhampton, QLD / Exmouth, WA/Burt Plain, NT) : October – March
Tasmania: November – February
The Nullabor Plains: June – October (this is Winter, but it is not so hot and it is also Whale Migration season).
Tropical Area’s (North of: Rockhampton, QLD / Exmouth, WA/Burt Plain, NT); May – October (this is the Dry Season)