I'd advise not keeping the bucks in with the colony, once they reach maturity the bucks will start fighting each other. They will also rebreed the does right after kindling which can leave the does in poor condition. Most people that successfully breed in colonies only introduce the buck for short periods of time so they can better control when they have litters.
NZ reach maturity at about 8 months of age. Does can often breed a bit sooner than that, though they have better growth rate if you wait until they reach senior weight before breeding. Bucks take a while to build up fertility. Also, these rabbits are not new zealands. New zealands don't have the harlequin gene or pointed white gene needed to make these colors. They could be new zealand mixes but they look like they have something in there as well, potentially californian and/or rex.