Ask HN: Intelligence and the time of day

I'm aware that a lot of scientific individuals read HN. I would like to take this opportunity to ask for feedback/possible explanations relating to intelligence and the time of day.

I'm a developer, I seem to solve most of my problems first thing in the morning between 7am-10am. During the first 3-4 hours of the day I solve most of my problems, problems I couldn't decipher the night before. I have asked other developers if they experience the same issue and most concur.

Is this a real phenomenon? Is there a scientific explanation for this?

I would love to find a way to extend my morning problem solving skills to the rest of the day.