Exterior paint doesn't just need to go on well. It needs to cure well, and that depends on the weather for the day you paint and the night after. In Central Ohio, the reliable window runs from late spring into early fall.
Most exterior paints want surface and air temperatures above about 50°F, and many need that to hold through the evening. Cold nights in April and late October can leave paint soft and tacky, or cause it to cure unevenly. Some modern paints are rated for lower temperatures, but they still perform best in mild weather.
Humidity and dew matter just as much. Paint applied late in the afternoon on a humid day can get hit by evening dew before it sets, which leaves streaks and weak spots. We start on sunny sides later in the morning, once the dew has burned off, and stop early enough for the paint to firm up before the air cools.
Direct summer sun can also be a problem. When siding is too hot, paint dries before it can level out and bond. On the hottest days we follow the shade around the house instead of fighting the sun.
If you want your exterior done this year, the best move is to get an estimate in the spring or early summer. That gives you time to pick colors and gives us room to schedule around rain, so the job gets done in the right conditions instead of rushed at the end of the season.