The research paper "Pressed for time: the circadian clock and hypertension" is completely free. It is a very technical read so I have cherry picked a few points and described them below.

This paper represents the scientific dialogue on this topic from about a decade ago. Back then it was realized that blood pressure regulation is in many ways tied to circadian rhythm health. Much of the talk back then focused on genes that act as clocks. Circadian clock genes control when other genes turn on or off.

For example, it was observed that the normal dip in sleeping time blood pressure disappeared in KO mice who had lost specific circadian-clock-genes. This dipping of pressure during rest time is a very important marker of blood pressure health as some hypertensive persons suffer from "nondipping" "overdipping" or "reverse dipping" during sleep time.

(Genetically engineered mice with specific gene(s) missing are called KO 'knockout' mice, and are used often in research settings. It is possible to remove, disable or replace specific genes, and then reproduce and maintain a continuous supply of such bred KO mice for experiments indefinitely, so to study the effects of that specific genetic KO.)

A decade ago, experiments surrounding the Light Dark cycles and hypertension were only being talked about in terms of what time during the 24 hour cycle, is best to take hypertension meds to achieve the best results..

Many unexplained mysteries were noted then, prompting questions such as does endothelial dysfunction causes circadian dysfunction or is it the other way around? (Click here for a more updated answer). Endothelial health is among a multitude of items that affects blood pressure.

So in conclusion, the main realization at that time was that circadian clock genes play a very important role in maintaining healthy blood pressure, but how to get these clock genes to assist in hypertension treatment was not known.

This article will be followed up with another using the findings from a more recent study, Stay tuned.