The coolest hour of the morning is usually at dawn, just as the sun is coming up. That's the best time to enjoy the sparkling dew and the beauty of the sunrise.
This is a great activity to do if you happen to have a drive-in movie not too far from home. The film takes place in the evening so temperatures are cooler and you can all enjoy the air. Many drive-in theater owners realize that part of the pleasure of visiting a drive-in is that the whole family, including your pooch, can enjoy the outing.