I do believe that there is an ideal time of day to go for a bike ride. The time that's optimum in pleasantness and fun.
In my experience, it's 3 o'clock in the morning. And let me tell you why!
Simply, there is virtually no traffic at all. You can ride on ANY street and go anywhere you want (just about) at 3am. I suppose that someone might say that they can do the same thing in the day. My rebuttal to that is that cycling in high-traffic areas is stressful and low on the pleasantness factor. At 3AM, you can ride along the busiest thoroughfares in a care-free frame of mind. You can explore your surrounding area without waiting for cars to pass before you cross a traffic lane.
There are obvious hazards when you ride at night. You need to have a brave and adventurous spirit to enjoy the ideal cycling hour.
I love riding downtown late at night. All the buildings are illuminated and there's virtually no one around.
Who can deny the existence of an IDEAL time of day for cycling?