New runner Denise recently emailed me asking what time of day she should run to beat the heat. She typically runs in the evening, but is willing to change her routine if she'll be more comfortable running at a different time.
When deciding when to run during hot, humid weather, you should avoid running during the hottest part of the day - from 10:00 a.m. to 4:00 p.m.
Although running in the evening is better than heading out in the middle of the day, it's hotter than morning running because the sun heats up the roads all day and they're still radiating heat in the evening. So you're better off running in the morning, before the sun comes up, if possible. If don't feel comfortable running in the dark or low light conditions, run right after sunrise.