It really depends on the hog, some won't hibernate properly until Dec or even Jan. This depends on many factors, but as long as there is food at hand (and they aren't under weight) it shouldn't be a problem. Their only predator's are badgers, man and extreme weather conditions - if you can call the weather a predator?!? ;o)
If they have found a perfect spot under your shed they will probably forage for food until the time is right for them.