They can come up and down depending on weather. Don't worry about feeding, instead put in some feeder fish and plenty of aquatic plants and let it go. They won't eat much even on warmer days until the weather is stabilizing. Your pond sounds a fine size, just make sure they have a substrate to dig in to, or at least some pot halves making places to get tucked into for hibernation. If your pond doesn't freeze, then you should run the filter all winter, or at least a pump with a waterfall or splash, to create some oxigenation.