DJ63, the sig says New Mexico. Do you have winter in New Mexico?? It depends on the region and what 'Winter' really means I suppose. In my area, most marina's want boats out of hte water. My marina requires I be pulled no later than Oct 15th. I usually shoot for the first week in Oct. Once I pull it, winterization begins. Funny about how the summer has flown by, I "Boat Winterization List" on my todo list sitting on my notepad right next to me as I write. I tossed it on there the other day. I'm doing similar to Roger. I make and check my list, then start pulling the stuff I need together well ahead of time.
As a general rule of thumb, I'd say winterization starts before you start getting hard freezes. Or when it is simply consistantly too cool to boat enjoyably.