Due to multiple factors, expect to potentially pay more when booking in December. For low rates, March can be a great choice for travel to Canberra. Flights to Canberra from Doncaster in March are about £1,360 on average during March, but can be found for as low as £901.
Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Doncaster to Canberra as you normally would.