Normally, when someone has been in NZ as a visitor for the longest period allowed (which partly depends on where they come from, and what kind of visitor visa they have), they aren't allowed another visitor visa until a comparable length of time has gone by, the basic idea being that you could have HALF your time in NZ as a visitor.
http://www.immigration.govt.nz/migra...aximumtime.htm
However, six months isn't the longest time he could be in NZ as a visitor - it's possible to apply to get longer.
http://www.immigration.govt.nz/migra...isitorvisa.htm But whatever you do, DON'T try and outstay whatever visitor visa he gets, or 'risk' anything, because showing up as an overstayer could jeopardize his getting the the residence through without problems.
Anyway, here's hoping all this turns out to be totally unnecessary.