Typically Cranberrys are used as dried beans. In that case you just let the pods dry on the vine, then pick and shell. They also are good as green shellies. These are picked as the pods change color and become leathery in texture. Mature but not dry. If you want them to look like the seed you planted, you will need to go for dry beans.

I'm assuming that you want to use them as shellies (green-shelled beans) which is probably their best use. The best indicator of maturity I've found is the pod color. When the red streaks on the pod begin to turn purple, then the seeds are ripe. You'll get the best cooked color in this stage. The seeds can dry very rapidly at this point - especially in your climate - so you'll want to pick at least every other day.

I agree with zeedman those kinds of beans are best as shellies. I grow green beans and shellies. I can buy dry beans in the gro. store cheaper than I can grow them and just as good. The green parts of the pod turns yellow and leathery when ripe.