For anyone wondering how our bodies synchronize to a 24-hour-cycle of the earth, it is primarily through light detected by our eyes. (A great resource for in depth: Professor of Neurobiology and Ophthalmology Andrew Huberman [0])

Apart from cone (RGB) and rod cells (brightness) which are responsible for vision in general (through the "-opsin" proteins: photopsin and rhodopsin, respectively) we also have a more ancient distinctive third class (subconsciously: not taking part in any vision at all) which was first discovered in the light-sensitive skin cells of the African clawed frog in 1998:
intrinsically photosensitive retinal ganglion cells (ipRGCs), which express their own distinct opsin—melanopsin. Melanopsin cells in mammals are specialized for measuring ambient illumination, contributing to visual discrimination, and driving a wide variety of physiological responses including, but not restricted to: synchronization of circadian clocks to light : dark cycles, regulation of pupil size, modulation of sleep and suppression of pineal melatonin production.[1]

So, even if you are blind those important signalling cells could be still intact. That's why one does not remove the eyes for 'cosmetic' reasons, anymore. This circadian feedback system functions ideally when all three parts of our photoreceptors are working in unison but can still function - albeit to a limited extent - if just one part is available.

To not confuse "noons" we can categorize those in three ways:

(i) solar noon: the time when the sun is at the highest point, at a specific day, at that exact location on earth

(ii) local noon: static time-zones i.e. conventionally set. Normally within +/-2 hours of the solar noon.

(iii) biological noon: adjustable through the light from outside but without any light input it varies from person to person (a "night-day"-cycle could be anywhere from 23.5h - 24.5h long).

There are roughly three time windows in which the photoreceptors of the eyes synchronize our bodies to the outside world, the first and last being the most important ones:

(1) After our physiological temperature minimum, normally about 2 hours before we wake up, naturally. Here the "biological noon" gets set, initially. The window closes some time about that point (I couldn't find a reliable number, anywhere, my guess is about 2 hours in, so about 4 hours after the "temperature minimum" the window closes and one is locked in the "dead" zone, for now).

(2) When the sun sets down. Experiencing the change and reduction in light helps the body to anticipate and prepare for the last window.

(3) In the last phase everything gets reversed, in order to not disrupt melatonin production ("hormone of darkness and sleep initiation") it is vital to not emulate the sun (bright, overhead). The best sources of light are low-hanging warm lights and just enough brightness to feel comfortable. Here, you have to take into account the adjustment period for your eyes. Unfortunately most people aren't used to see adequately and orient themselves in low brightness settings (peripheral vision). Star-gazing could serve as a starting point for some sensibilization.

Those biological insights can be used to balance and fine-tune one's circadian rhythm.

But the most reliable and effective way in getting the system into full gear, is how this elaborate system evolved in the first place: outdoors. Living outside for a couple of days, on some weekends of the months for example, to "reset" can work wonders: a substantial set of people who think of themselves being night owls are actually fooled into it by artificial lights ;) [2]

[0]https://hubermanlab.com/find-your-temperature-minimum-to-def...

[1]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3619500/

[2]https://www.cell.com/current-biology/fulltext/S0960-9822(13)...