Biologically, the optimum would probably be more time fiddling, adjusting the clocks daily so that sunrise is at the same time every day. That would sync the clocks to one of the most important environmental factors that sets circadian rhythms.

Offhand, I can't think of any biological significance to noon. Noon's charms for timekeeping are technological.

1. It is easy for everyone in a given area to agree on noon. It happens with the Sun high in the sky, as opposed to sunrise which is obscured for many be trees, hills, and buildings.

2. The interval from noon to the next noon is constant [1]. The sunrise to sunrise interval varies considerably. Make a good mechanical clock and sync it to noon, and it can run a long time without getting too far out of sync. With time based on sunrise, you'd need to adjust the clock everyday, or make the clock more complicated to have it know about the variation.

[1] well...maybe not to people with very precise clocks, but it is constant as far as the needs of most people most of the time goes.