"But how does the body sense the difference between 8pm when it is first dark and 4am , two hours before sunrise? Eyes ? no. Ears? Taste? Touch? Smell?"
Advanced level question, I have no advanced answer; could be our tiniest hairs in the ear or nose, similar to “nanomechanical oscillations” (vibrations on the tiniest atomic or molecular scale) that plants have.
Who govern whom; the pineal or the thyroid. I suggest they are inter connected.
The combination we suggest here at the forum, Iodine governing the thyroid, boron the parathyroid (calcium metabolism!) is like an intertwined couple, they do not work well without the other half.:)