My approval literally took a few days. I had expected a week or two and I think it took 3 days. I had an immigration advisor and they submitted the paperwork for me once I got it to them. My advisor laughed at us because we had so much paperwork though. We thought it was normal but they said we were "very thorough".
My advice is to make sure all your bases are covered. We probably went overboard, but we submitted phone records (not just the bills but the actual call record proving how often we called each other), text message history (a pain to extract but worthwhile IMHO), letters from friends/family, a letter from my landlord, regular pictures, bills, etc.
I applied for my residency at the same time as my work visa. We had only been living together for about 6 months when I did the Work Visa application but the advisor said that if we submitted both at the same time it would make me look more committed. Since you have to live together for a year before you can get partnership-based residency, I moved to New Zealand once I got the work Visa and we kept sending proof of our relationship until the 1 year requirement was met and then I got my residency.
One challenge for me was that they only gave me a one year Work Visa. That limited what benefits I could get (
https://lifeinnz365.com/2016/07/11/g...ed-healthcare/) and can be a problem for some companies when hiring you. It all worked out for me but I wasn't covered under the government healthcare until my residency came through and the company I work through pulled me on as a 'fixed term employee' rather than truly permanent until the residency was done.