Paint does not simply dry, it cures. The film forms as water or solvent leaves and the resins knit together. Below about 50°F that process slows down or stops, and a coat that never fully cures stays soft, holds dirt, and peels early. Some modern acrylics are rated down to 35°F, and they genuinely work, but they still need the surface to stay above that temperature while curing.
The number that catches people out is the overnight low, not the afternoon high. A 62°F October afternoon feels like painting weather, but if it drops to 38°F at 2am the film is still curing when the temperature crosses the line. That is where you get a finish that looks fine in November and fails the following spring.
Dew is the other autumn problem. As nights get colder, moisture settles on siding early in the evening — painting late in the day in October can trap it under the film. In practice that shortens a usable autumn day rather than the season.
Sun angle matters too. A south wall in April can be well above air temperature and perfectly paintable while a north wall in the shade is not. Working around a house through the day, following the sun, is normal practice rather than a nicety.
What this means practically: exterior work books from late spring through early autumn, and the last comfortable stretch is usually late September into early October. If you are hoping to get an exterior done before winter, calling in August beats calling in October.