I don't remember seeing anyone on the threads who had applied for one of these, so I don't actually know the answer from anyone else's experience, so I've been looking at the INZ sources online.
Looking at WH3.10.5 a, here
https://www.immigration.govt.nz/opsmanual/#41770.htm, it looks as though, if a visa is granted, it will run for six months, regardless of what visa the applicant was holding before s/he applied for the SSE visa.
Here's the INZ information page about it.
https://www.immigration.govt.nz/new-...-sse-work-visa