https://www.immigration.govt.nz/new-...s-visa-holders See the Criteria tab near the bottom of the page for what is required for a partner-sponsored visa. Notice, the requirements for proof of living together are the same for a partner-sponsored work visa or visitor's visa, and though no length of time is mentioned, we know from experience that INZ take applications seriously which have 2 - 3 months' evidence.
See old threads
https://www.google.co.uk/#q=site:enz...tnership+proof for discussion and examples of evidence of partnership.