Exterior paint doesn't cure by drying in the way most people assume. The film has to coalesce, and that process depends on temperature and moisture, including overnight. This is why a coat that went on during a warm Rochester afternoon can still fail if the temperature drops into the forties before it has set.
Most exterior products are rated to a minimum application temperature, and the number that matters is the low, not the high. A day that peaks at sixty-five and falls to thirty-eight overnight isn't a paint day, whatever the afternoon felt like. Around here that gives a dependable window from roughly late May through September, with shoulder weeks on either side that depend on the forecast rather than the calendar.
Moisture is the other half. Siding that was rained on yesterday can still hold enough water to stop paint from bonding, and morning dew on a north elevation lingers longer than most people expect. Washing a house and painting it the same day is one of the most common reasons a job fails early.
If you're calling for exterior quotes in October, the honest answer from a contractor is usually that the prep can start now and the finish coats should wait. Scraping, wood repair, and priming with a product rated for lower temperatures can often proceed later into the fall than the topcoat can.
There's a practical upside to the seasonality. Winter is the right time to book interior work, remodeling, and carpentry, and it's also the easiest time of year to get on a good crew's calendar. Plan the outside for spring, and use the cold months for the inside of the house.