I usually ride in the evening a little bit before it gets dark outside. I don't like to bike in the dark, but throughout the day I have too much on my plate to be able to go out. I know people often recommend doing exercise like biking first thing in the early morning but I like to sleep in, have breakfast, and jump right into my day. I figure going in the evening is better than not going at all! Usually I go right before supper time.
Some days I go at different times though. I don't really have a set time at all, just whenever I feel motivated and ready to go.