We eat at Kona for breakfast (on our MK day) every trip. We're usually there on a Sunday, in May and Sept., around 8:30AM or so. We never make PS and our wait ranges from none at all (which is most often the case) to a max of 10 minutes. It can sometimes look very crowded just outside Kona and you find yourself saying "Oh No!!"
But then you get near and find out it's mostly folks with kids waiting to get in O'hana.
But antnee is right--to be absolutely safe ( if any sort of wait will disrupt your plans) a PS might be nice.