Archaeologica.org

TRANSLATION
Fifteen laghus make one näòikä, which is also called a daëòa. Two daëòas make one muhürta, and six or seven daëòas make one fourth of a day or night, according to human calculation.

Fifteen laghus make one näòikä, which is also called a daëòa

One day - 12 hours
One night - 12 hours

from Kak's article

This statement could either relate to the speed of the sun or to that of light. The units are well known. For example, the Indian epic "Mahabharata", conservatively dated to 400 BC - 400 AD, defines 1 nimesha to be equal to 16/75.3 seconds; 1 yojana is about 9 miles ..

Like most Asian calendars Indian calendars do not employ the solar year and day (i. e. tropical year and solar day) but the sidereal year, and the Synodic month(29.5306 days). Thus, the calendric year based on the sidereal year is defined as the time between two successive passes of the sun through a certain star's circle of declination. Lunar days and sidereal months are also used, and in certain lunisolar calendars lunar year and lunar month are taken into account, too.

Astronomical knowledge of Ancient India was written down in scientific treatises, called Siddhantas. In them, values for the lengths of months and years were given representing the latest knowledge at the time the Siddhanta was written. The values range from 365.258681 days in the Âryabhatiya to 365.258756 days in the Surya Siddhanta and are all too long compared with the modern sidereal year length of 365.25636 days. Nevertheless they are still in use for Indian calendars today.

The sidereal month is about two day shorter (27.3217) than the Synodic month.

As mentioned earlier, to account for the difference between the solar and lunar year an extra lunar month occurs about every 2 ½ years as “Adhik Mas”.[1][1]

According to the Moslem calendar which is widely followed in Middle East and in other Moslem countries the lunar year is strictly based on twelve lunar months of 354 days per year. That’s why their holy month of Ramadan occurs by approximately 11 to 12 days earlier than that in the preceding year.

The solar day (commonly referred as the “the date” in western calendar) has a fixed length of 24 hours. The change of date occurs at midnight as per local time or standard time of a given local time zone. Thus, the date changes from midnight to midnight. Similarly the day (as in weekdays) changes from midnight to midnight as per local or standard time for that location. In other words, as per the western (or English) calendar the length of day and date is exactly 24 hours, and there is a definite correspondence between the date and the corresponding day of the week.

A lunar day usually begins at sunrise, and the length of lunar day is determined by the time elapsed between the successive sunrises. As per the Jewish calendar their lunar day begins at the sunset, and lasts through the next sunset. A lunar day is essentially the same as a weekday. In India the lunar day is commonly referred as “War”. Just as the English calendar has seven days for a week, the Indian calendar has seven wars for a week.