Remember it can take 24 hours to fly to Australia and 24 hours to get back again (flying time) so you can easily lose 2 days at either end of your holiday with the flights and time zone differences.
My wife flew to Australia earlier this year and left the UK late on Monday and did not land in Australia till Wednesday (with 24 hour flying, plus a break in Dubai for a couple of hours, plus going forward with the time zone).
I think a 7 day holiday in Australia is a waste of time, or even 10 days really.