Ian,
I am aware of at least four Kiwi?? who were granted about six months leave to travel home to New Zealand. The six months included travel time of about 6-8 weeks each way.
They were Eliot King, Maurice Buckley, Phil Fowler and Les Brake.
The interesting thing is that all were granted their leave in 1918, all were RAF ex-RNAS and all were, or were recently serving in the Mediterranean theatre. This may be a reflection of the particularly debilitating climatatic environment their service was being carried out in?
Errol