It's about a 4.5 hour flight from Christchurch to McMurdo base in Antarctica. The absolute, shortest path from the south island of NZ to the closest point in Antarctica is around 1500 miles. There are a few islands closer of course, and the Drake passage between South America and Antarctica at the tip of Cape Horn is only about 500 miles wide, but there isn't really any infrastructure on that side of the Antarctic continent. New Zealand is a good choice if you're going to be traveling to Antarctica often.