I'd rather have them on a bit early and get a little extra wear on them than get caught in snow with summer tires. I usually throw mine on the end of October just to be safe. I figure if I plan to get them on by the end of October and procrastinate a little I'll still have them on in time for any November snow. Waited too long a few years ago and still had the summer tires on when we had that fluke storm in the middle of November that basically shut down the state.