Hiked it In Jan 2005 - geautiful track, we found it really easy. We did it in just over a day - it is only 22 miles I think, with one big ascent in the middle, but very good smooth, wide trail tread. Well worth doing the 30 min detour in the middle from one of the passes up to a nearby peak (sorry, can't remember the name, but its from the big pass with a shelter at the top).
Theres also a number of great rivers and waterfalls - I'd recommend having some swimming kit. We swam at the really big waterfall near the end, which was a bit like being hosed down with a pressure washer.
We camped, but the huts are really nice and not much more than the (?NZ$15?) camping fees. We went a few miles in the first evening, then did the rest of the track the next day, and came back down the caples over the following 1.5 days.
If you have time, we thought the Kepler was the nicest of the tracks overall - we did the milford, Kepler, routeburn, caples, queen charlotte and Tongariro crossing. Kepler was also a 2-day affair for us.
Obviously, time is a function of speed & how long you're going to walk for, so you may find that the Dept of Conservation (who manage the tracks and give out the permits) recommend much longer times. They were very reluctant to issue us permits that required walking more than 12 miles a day.
