On an accredited employer visa the partner gets a work visa to match the main visa holder's visa so the length is the same.
After 24 months you can apply for residency. If you earn more than 90,000 you are given PR. The other visa holder is too, so your wife can then go from a work visa to Residency/permanent residency based on your salary.
If she gets an initial visa based on your accredited employer visa she has to activate the visa within a certain time so has to come to NZ but doesn't have to stay.
This information is just based on our personal experience. Details may have changed.
Good luck!