Thanks for the reply.
After further digging into this story, I found out that:
(A) it was more than just a few hours travel -- almost all one day would be spent on the trip, counting a stop halfway.
(B) the military gave them 7-day furloughs, rather than weekend passes.
(C) Darwin was pretty much a "dry" territory (girls, liquor & beer) while Adelaid was more accomodating to thirsty & adventure-seeking GI's.
(D) so, even losing 1 day travel down and one day on the return trip, they still had 5 days to spend in a city not as threatened for attack, not as "militarized", and could offer more to a soldier on leave.