I would wait until there is no more chance of frost to set them out, as I have heard hardy kiwis are easily damaged by late frosts.
http://www.fruit.cornell.edu/m...
Edit: The problem with hardy kiwis isn't how cold hardy the plant is, but more that they evolved in climates with more predictable temperature transitions than experienced in North America. Some species of kiwi tolerate Siberian winters, but will not tolerate cold snaps in spring in Southern Canada or the US North East.