most nzw's will breed starting at 5 months old,if the does are overly fat or thin they generally will not breed.A few minutes is all you need to put them together,leaving them along or a couple of days together could end with a neutered ,or even dead buck,to hot and they will not breed or if they breed the mating will be infertile,very, very seldom some does and some bucks just will not breed,