Start slow! I had to abandon running in my five fingers after a few months because of calf cramps - for 2 months I couldn't even run one block without my calves cramping up - but I started out running 5 milers in them. I'm not familiar with those specific shoes, but my recommendation would be to start at 1 mile, or even half mile distances and increase distance very slowly, perhaps by as little as half a mile or less a week. The second time around, I was religious about this strategy and am up to 7 miles barefoot, injury-free and loving it!
Don't think of those shoes as an end but as a step towards going truly barefoot. It's a beautiful thing. Good luck!