My 1st batch (the pic of the bottle) I left the cranberries in for only a week. In the batches I just made, I left them in for two.
The biggest problem with the cranberries is keeping the fruit cap wet. With more sugary fruits, fermentation goes crazy. I've had to clean strawberries and blackberries out of the carpet and off of the walls... But cranberries don't do that, so they just float on top. You will want to "push down" the fruit cap twice a day so that no mold forms. In addition, you want to make sure you are not introducing a lot of oxygen to the secondary. We ended up getting one of those carboy mixers that you attach to a drill. It made things a lot easier. You just have to try not to agitate the top too much.