Noon is the only easily measurable time point in the day that is always (approximately) 24 hours apart. Also, sunrise and sunset are always symmetrical to noon, even when the day length varies considerably. For setting up a time system, noon consequentially is the correct reference point. But yes, your day rhythm will vary relative to that across the year, but there will differences according to local (like latitude) and personal environments which will make sunrise not a good reference point for a time system.
> Noon is the only easily measurable time point in the day that is always (approximately) 24 hours apart.
DST resets the time to move noon closer to sunrise, not closer to midday. There are currently 4h30m before noon and 7h30m between noon and sunset. In the middle of summer, it's 6h30m before and 9h30m after. Noon isn't well indexed at all.
