Best time to exercise??

I prefer running in the evenings (7-9pm) - first of all I am not a morning person, second - it's usually cooler, and third - it helps me to erase all the day thoughts and worries. However,once a week I wake up before 6am to get to the pool - it's the only time of the day which works for me and swimming is one of my favorite exercises, so it's not that difficult to motivate myself to get out of bed...