If we have a solid morning, we will have a solid day. A chaotic morning will bleed into a chaotic day. This is the real reason behind the idea that people who get up early are more productive.
It’s not the time, it’s just that at that time, our bodies have been trained to get up and get rolling into our day. Whereas waking up at 11am feels like you’ve lost half the day and we tend to rush through a jumbled mess of rushing to get started with our work to make up for the lost time. Then we have a terrible and unfocused day.
If we agree that we each get eight hours of sleep every night, who cares if you get to bed at 9pm and wake up at 5am and I prefer going to sleep at 2am and waking up at 10am?
Without getting into the science surrounding the circadian rhythm, I tend to believe that it is the solid morning routine that sets you on course for a productive day, NOT the hour at which you awake.