Otherwise you need to draw a line on exactly the other side of the world to Australia (and Australia spans two time zones so it's not an easy task) and make THAT your 'date line'.
in all honesty the statement i made on the other thread about having a team member post from overseas (greece) was very much tongue in cheek as far as i am concerned the challenge is Australian based...
Thought about it more overnight, and same day would involve a lot of extra work. Sticking with GPS date is much easier and less confusing.
And a "day" can easily be considered as starting at 0000 from the International date line, working it's way round the world to end up at 2400 back at the IDL.
For some reason I was thinking of "day" as the period of local daylight.
I have no problem either way for team members sailing anywhere they happen to be. (as long as it's not on a land/ice-yacht)