@donny young - if what you have been doing has been working, I wouldn't worry about changing.
We keep our pond running all winter long, so it's not something I actually worry about. I get everything cleaned up and ready for winter before Thanksgiving - some years that's perfect... other years it's just a bit too late! As you know in the midwest when winter "starts" can be anywhere from late October (like last year, when we had six inches of snow on Halloween!) to mid-December... we had 70 degrees here near Chicago just 10 days ago! So there's no way to pick a date and stick with it from year to year if you are hoping to let the pond run as long as possible. For most people it works best to pick a day when you can still work outside, before it gets too cold or snowy.