I canīt help you with the Australian part of your cruise, but I can with the NZ part since I am a Kiwi, albeit now living in Spain.
The time of year you are going is the beginning of the summer over there. However, NZ has a very unpredictable weather system, because it is just a couple of small islands in the middle of almost nowhere. For this reason you can get four seasons in one day! This of course doesnīt happen every day but it is common.
However, it is the most beautiful country and the people are very friendly. I donīt know what excursions you are being offered but the scenery all over the country is just lovely. Hopefully there will be an excursion to the Southern Alpes, and to the lakes in the south island too. Dunedin in a very pretty city. Itīs where I was brought up so I have a soft spot for it. Iīm sure youīve been looking on the internet to see what else there is.
Hope this is a help. Iīm so envious of you with this cruise!