it's nothing you can put a number on, and I have no experience with oreganus, it may or may not happen. I know that my cerberus, (which are distantly related to oreganus)that came from right here near my house at the 7000 ft. level shut down automatically in Sept. no matter what I do. There really is no reason to be scared. I think it stresses the keeper more than the snakes when they shut down early. As long as the snake has been well fed during the summer it should be fine. The main thing is to be prepared for what may happen and learn to read your animal. The mistake most people make is to keep the snake up and to keep attempting to feed it. The snakes usually cruise the cage restlessly and burn calories they shouldn't be burning. Once the snake refuses a meal mark the date. If it continues to refuse meals for one month after that date (this gives the time needed to clean out the digestive tract)put it in the coolest place possible until the weather changes and you can put it down for the winter.
As for breeding crosses I have no experience. It shouldn't be too difficult. Is your snake already a cross (oreganus X ?) or do you plan on breeding it with something different? I personally wouldn't recomend it. Wild hybrids are an interesting novelty and I would probably keep a neat looking one but thats it. Captive bred crosses only create confusion in the hobby. Follow the forum down and look at some of the earlier posts. There are cases where people bought snakes as mojaves which were really atrox X viridis, the same person crossed an oreganus and a lutosus but the snake looks just like an oreganus. If that snake for some reason ever ended up with a dealer it would most likely be sold as an oreganus and then some unwary buyer could end up polluting his gene pools. If your female is pure oreganus I would just get her a male oreganus. Males reach sexual maturity much quicker than females so things would actually time out about right for you. Female cerbs first reproduce at about five years of age, males can start at about 18-24 months. I would think oreganus would be similar.