This is a good question.
It has been my experience that the principle of the circadian clock is accurate, but I do not think it is absolute at least in the west, because a la western individualism, every body is different.
The accuracy of the principle is even proven by something as gross and unsubtle as heroic, allopathic medicine which shows that the time of death of those suffering from fatal diseases or conditions is clustered around four o'clock a.m.
Of all the modalities available I have found that for myself Chinese acupuncture and western herbalism work the best. The least effective is homeopathy except in one very interesting regard: In a homeopathic diagnostic questionnaire, I have found remarkable accuracy in those inquiries as to what time of day the symptoms are the most, what time they are the least, at what time the patient expresses a need for something (such as fresh air,or a darkened room), at what times they are desirous of hot liquids, or cool liquids, and so on. This is complicated by the elemental typology of the patient. For example, a Phosphorous type is going to show difference symptoms and different needs and rejections at different times than a fairly similar Lycocodium type who is suffering from the same problems. If the homeopathist knows what they are doing and can keep all those balls in the air, then the diagnosis is spot on whether or not the remedy is effective. I have seen a homeopathic diagnosis with a western (or in many cases Chinese) herbal treatment to be remarkably effective. (The only time I have experienced an effective homeopathic remedy for me was one against a Black Widow spider bite.)
In line with this also is the timing of the treatment. My wife who has been practicing Postural Integration
body work for the past thirty years, just told me she does her best work at 11 a.m. and 2 p.m....Tuesdays. Good god...now she just told me what the Ayurvedic circadian clock might show for this and that and my eyes are glazing over.
"A lonely impulse of delight drove to this tumult..." W.B. Yeats