On Level Orange Ozone Alert days in Dallas, TX what time is best to take a walk for health?

Ozone is produced by visible violet and more energetic light from the Sun, from other components of smog. Ozone is decayed by time, temperature, and humidity. So if you do your exercise before the Sun makes more ozone, maybe even before car emissions have climbed to be able to make more ozone (so before morning rush hour), that'll be your best time.