I think that the best time to go cycling is in the early morning. For me, in any case, it helps me you wake up and I feel that I have more energy throughout the day after I've cycled in the morning. However, I cycle in the morning mostly because my schedule only allows me to cycle during that time. So my actual answer would be that you should cycle when it's most convenient for you, and when you are stressed out the least. That will make the ride much more enjoyable and much more fulfilling.