Unlike Vancouver, you do NOT pre-clear US customs in Kelowna - you'll be doing it on arrival in SFO. So naturally this will take more time.
However, if your flights are all on the same ticket (booking reference etc), the airline must feel it's a valid connection, and you should be fine - if you're not, they'll have to rebook you.
However, if you don't want that hassle (next flight to Auckland may be a day later, or worse), or you have separate tickets, or think it may take longer for you to go through (do you have a snowboard bag etc?), or are concerned that you may be late leaving Kelowna (weather, for example), then you may want to try and make an earlier flight from Kelowna.
SFO is a really nice airport (in my opinion - I've even slept overnight in it), it's nothing like the transit nightmare that is LAX, but if there's a long queue you may still be cutting it really fine to get through, given you have to go through US immigration once you arrive, even for a 'transit' flight.
(source: NZer myself, with experience transiting in LAX enroute to Auckland, and I've had several flights in/out of SFO, although not internationally connecting there).
Additional source: Australian Frequent Flyers: they note that fog can be a big problem at SFO, and if you can't land you may miss a connecting flight. Suggestions there are 3 hours minimum.