Alain Daniélou wrote Music and the Power of Sound, The Influence of Tuning and Interval on Consciousness and a footnote in this is of interest regarding the role of the tritone in India. The trigger was a request to review a new book about Harmonic Geometry by John Oscar Lieben, which quotes a footnote in Daniélou, page 156:

51. The use in Indian music of the augmented fourth, or tritone, at the criti­cal times of midnight and midday reminds us of the magical importance attached to those hours, and of the use of the tritone (diabolus in musica) by Western musicians for the representation of magic, which is nothing other than the possible intersection, at certain critical hours, of worlds that can­not normally communicate. It is used conspicuously in this way by Schumann for the character of Manfred, by Wagner every time a magi­cian appears, by Berlioz in the Symphonie fantastique, by Weber in Der Freischutz, and so on. In Chinese music the Iü rui bin, corresponding to the augmented fourth, represents the summer solstice, the critical mo­ment in the annual cycle when the masculine influx, hot and creative, gives place to the feminine influx, cold and destructive.

The tritone plays an important place in the work of Ernest G McClain's classic work The Myth of Invariance, informed by his contact with Antonio de Nicolas who studied the Indian tradition as habing been concerned with harmonic audition rather than extensive vision. Agni, the Indian god of fire, plays the role of tritone within harmony by enabling creativity as a liberating counter to cosmic and human egoity. I wrote this summary document; of what Ernest McClain wrote about Agni. With this in mind one can return to Daniélou's main text:

The Periods of the Day

Much importance is attached in Indian music to the connection between ragas and the periods of the day. Westerners recognize that certain musical works can represent morning, midday, or night, but they have never tried to define the intervals by which they are characterized, and they find it quite natural to play them at any hour. Indians do not approve of such a lack of sensitivity; ragas of the night should be played at night, and those of the dawn at dawn. Only then can we fully understand and enjoy them without effort, because we ourselves change according to the hour, and the day in its brief cycle is the image of life.
Played at times other than those which they represent, ragas can for a mo­ment change the course of nature; musicians playing the ragas of night during the day, for example, have been seen to appear gradually surrounded by intense dark­ness. This connection of ragas with the hours of the day is also known to the Per­sians and Arabs, but their calculation is not as precise as that of the Indians.

There are three main divisions of the day:

1. The day, of which the sun is the luminary
2. The night, of which the moon is the luminary
3. The twilight, of which fire is the luminary

The sun is said to have 116 rays, the moon 136, and fire 108. Their sum is equal to 116 + 136 + 108 = 360. To this corresponds the division of the day into 360 units of four minutes each. Six of these units form one ghatikä of twenty-four minutes, of which there are sixty in twenty-four hours. These have been con­nected with the division of the octave into commas. Twelve of these small units form one mubürt, of forty-eight minutes, of which there are thirty in a day, each of them being dedicated to a partimlar deity. The day is further divided into eight watches (praharas) of three hours each and, further, into twenty-four hours (twice twelve), assimilated to the twelve regions of the octave, the signs of the zodiac, and so on. The day and the night comprise an ascending part, of masculine char­acter, and a descending part, of feminine character, because "manifestation or growth is masculine, disappearance or decline is feminine, and neuter is the intermediate condition."50 All these elements have their importance in determining the proper time to play the different ragas, principally regulated by the respective value of the notes in regard to sun, moon, and fire. The main divisions are therefore:

1) Sandhiprakasa ragas, for the conjunction of the day and night (sunset and sunrise), whose general characteristics are Re komal (I\) and Ga tivra (E natural)

2) After Sandhiprakasa (first part of the day or night), usually characterized by Re (D), Ga (E) and Dha suddha (A natural)

3) Before Sandhiprakasa (second part of day and night), characterized by Ga komal (Eb) and Ni komal (Bb)

These periods are further defined by the following particularities:

1. Between midday and midnight the viidi (dominant note) is in the lower tetrachord (purvanga), i.e., between Sa (C) and Ma (F).

2. Between midnight and midday the viidiis in the upper tetrachord (uttaranga), from Pa (G) to Sa (C).

3. The augmented fourth, Ma tivra (F#), belongs to the critical times of midday and midnight, sunrise and sunset, solstices and equinoxes. It may also exist in the morning, but then it is dominated by Ga komal (Eb). There are some exceptions to this rule, when Ma tivra (Fl) corresponds to an expression of fear and pain.51

4. In the defective modes of six or five notes, the evening modes never leave out Ga (E) and Ni (B) (udatta notes), and the morning modes never leave out Re (D) and Dha (A) (anudatta notes).