That's a lovely chart, but it doesn't seem to be using solar time? I wake just as the sun stretches over the horizon and peeks though my window. In the summer, it's very early; in the winter, it's quite late.

If we're to set the start for the official day, it should probably happen an hour or so after the sun has risen. Sadly, on the western side of time zones, like Grand Rapids MI, it's often pitch black when the workday starts.