Siddhanta Shiromani (Crown of Treatises)

...[measures of] Minutes of arc kalā and Seconds of arc viliptā. Just as a Year varṣa has divisions such as Months māsa, Days dina, Ghatis a unit of 24 minutes, and Palas a unit of 24 seconds, in the same way, a Zodiac Sign rāśi literally "a heap" or constellation has divisions of Minutes kalā and Seconds vikalā. This means that this system of time division should be followed hereafter. Now, [the author] states the measurements for the Solar Day saura-dina and Solar Month saura-māsa:

The term Revolution bhagaṇa refers to the Sun's movement through the entire circle of the zodiac. The time it takes for this to occur is the measure of a Solar Year saura-varṣa. Because the planets situated in these revolutions have a fixed eastward motion, even the "crooked" retrograde planets' eastward transit through Aries and the other signs is counted. Any westward movement caused by Retrogression vakra is considered an anomaly vikṛti of the planet and must be accounted for. Since the Sun and Moon never undergo retrogression, they possess only eastward motion.

According to the definition of time division stated here, a Solar Month is a one-twelfth original: "daśāṃśaḥ" (tenth part), though context and astronomical standard suggest "dvādaśāṃśaḥ" (twelfth part) part of a solar year. A Solar Day is a one-thirtieth part of that month. A Solar Ghati is a one-sixtieth part of that day. Its sixtieth part is a Kala, then a Vilipta, and so on.

That same single year is a Day and Night for the Gods and Demons deva-asura. In that cycle, when it is day for the Gods, it is night for the Demons. Likewise, when it is day for the enemies of the Gods Demons, it is night for the Gods. As will be explained in the section on the Sphere gola Celestial mechanics/Cosmography: "The Sun revolves around the half... all the thirty Gods see the Sun once it has reached Aries... while it moves in the southern hemisphere [it is night for them]." Similarly, it is said that the Sun "revolves in the middle for the Gods, but moves counter-clockwise for the enemies of Shiva the Demons." From this principle, the calculations for the months, years, and ghatis of the Gods and Demons are to be performed.

Next is the Lunar Month cāndramāsa. 1