A work permit can be issued fairly quickly if you have everything in order. We got ours in 45 minutes--we had a ITA number for them to reference which may have made a difference. They couldn't see exactly what we had submitted but just that we had submitted it. In the Christchurch office at least you can expect an appointment the same day you go in (Go early, even at opening time you can expect to have 10 people in line ahead of you).
Anyhow I
think that if you have a job offer you should be able to get a Essential skills work visa or Talent visa that allows you to leave the country and return for the purpose of work. You will want to look at the work visa form on the NZIS site. There is a multiple entry box to check on the form.
http://www.immigration.govt.nz/NR/rd...8FA/0/1015.pdf
I don't think that the employer has to be accredited unless you are applying for a job that is not on the long term skill shortage list, ie a talent visa.