Awww , bless them , don't forget their body clocks are still working on Aussie time difference. When I came here from Australia it took me a while to stop falling asleep too early.
a day per hour of time difference minus three hours (ie 7 hours difference, 4 days). However, activity in daylight, and occasional naps, can speed it up. The best way to speed it up it to slog through a day regardless of how bad you feel, then collapse, hoping you don't get hyper
Don't forget Australia is a bloody big place and covers several time zones, so whilst it might be 7 o'clock (and dark) on one coast (Perth, West coast), it might be gone 10 on the other coast!! (Sydney, East coast). Also it varies by season and the angle of the sun - just like here. At the moment it is mid-winter in Australia, with the associated shorter daylight hours.