New Zealand Timeframe
 

My wife and I would like to visit New Zealand but we are not sure of a reasonable amount of dedicated time to get the most out of it. Generally we just like the outdoors and are not much into the city life. Any help would be appreciated.

3 weeks. 2 in the south island 1 in the north.

However, you could easily spend a lot more time in NZ.

Because NZ is so far to travel from Canada and the fares so expensive, I felt that I should spend a minimum of a month there. This turned out to be a good amount of time. Although, I could easily have stayed much longer. But I feel a month gave us a chance to see some of the top sites , as far as scenery goes.
It was a wonderful trip.

Having been to the South Island on six different occasions (North Island once), I can honestly stay that there never seems to be enough time!

Our trips have ranged from 12 to 28 days and we always seem to leave wanting more.

Having said that, three to four weeks should give you a good feel for both islands. If you only have two weeks to work with, I'd suggest concentrating on just one island and personally, my choice would be the South.

The South Island has fewer cities, is less populated and has an abudance of outdoor pursuits.

Have fun.

We did a three week trip in the South Island - this gave us a little bit of time to do some hikes and not feel too rushed. 4 weeks would be good - 3 for the South Island and 1 for the North Island.

We spent three months in New Zealand last year and still want to go back to see more.
If you're into the outdoors and have a limited amount of time, I'd recommend the South Island - exceptionally diverse beauty ranging from the wild west coast to the rugged beauty of the Catlins to the stunning colours of the Queen Charlotte track and Abel Tasman area.
Swim with dolphins, go for long hikes, revel in deserted beaches, sample great wines and enjoy!

The time of year will affect your travel plans. In the NZ winter (July and August) temperatures can be quite cool on the South Island. We spent one cold day in Wanaka with a high temperature of 2 degrees Celsius. Highs on South Island are generally in the range of 8-10 degrees Celsius in the winter. The North Island is warmer by 4-6 degrees Celsius during the same season. If the temperatures are a concern, you may want to increase your length of stay on the North Island.
I agree that the South Island has more to offer, and that a one month stay is ideal for NZ.