Spring skiing is Septemer. Our season starts proper in July, typically July/August are winter conditins. But our winter conditions are mild compared to North America.
Do a search here to find other postings on NZ, and look for Spindrift's NZ trip report.
What type of skiing do you like? off piste, groomed, back country. If you are advanced and have a reasonable level of fitness you could try the club ski areas not 'club' as in 'exclusive' but small areas run by skiers, minimal amenities but heaps of character. They have rope tows which are very tiring and no groomers, but on the plus side there is uncrowded slopes and lots of terrain.
to get you started check outwww.snow.co.nzwww.chillout.co.nz
(has info on rope tows so there are no surprises see 'nutcackers')
my favourite commercial area is Treble cone, staying wanaka www.treblecone.co.nz
my favourite club area is Craigieburn, can stay on the mountain but need sleeping bag www.craigieburn
I recommend to plan holidays for August, it is the most reliable month. metimes we have good seasons early, some late. But mid to late August is when I plan my holiday, is the most reliable. Last year all our snow came after the areas closed in October - blame global warming