I fish Lake Ontario.
When I still owned a rig with an outboard engine, I delayed winterizing until the beginning of December. When I changed to a 3 liter mercruiser, I usually just drained all the water out, but went on fishing and again did not winterize until the beginning of December. That is mostly because the brown trout tend to get close to shore in 30 or 40 feet of water near the creeks that they swim into for spawning and because I know the exact location of some under water springs that produce relatively warmer water than the surrounding water, fishing this period is very attractive.
Now, however, I run a 4.3 liter cobra and the far more complicated cooling system makes me nervous and I will probably will winterize within the next few weeks.