The measurement of time

Time is a unit of measurement that measures the span of an object's existence.
In the material world, it is dependent on planetary systems and the Universal Ages.

The measurement of time for rituals and activities

1 सूर्योदय Sūryodaya Sunrise
2 सूर्यास्त Sūryāsta Sunset
3 चंद्रोदय Chandrodaya Moonrise
4 (मास) (Māsa) Lunar month (see below)
5 शुक्ल / कृष्ण पक्ष Śhukla / Kṛiṣhṇa pakṣha Bright / Dark fortnight
6 तिथि Tithi Lunar day
7 नक्षत्र Nakṣhatra Asterism or lunar mansion

For its use, see below.

The "small time" in Veda (Bhagavat Puran 3.11)

1 diva-ratri (day and night) - 30 muhrta
1 muhrta - 48 min
1 danda (nadika) - 24 min
1 danda - 24 min = 15 laghu
1 Laghu = 24/15 = 1.6 min = 15 Kastha
1 Kastha = 1.6 /15 = 1.6*60 sec /15 = 6.4 sec
1 Kshana = 1 Kashta /5 = 6.4 /5 = 1.28 sec
1 Nimesha = 1 Kshana /3 = 1.28/3 = 0.42 sec
1 lava = 1 nimesha /3 - 0.42/3 = 0.14 sec
1 vedha = 1 lava /3 - 0.14/3 = 0.0474(074) sec
1 truti = 1 vedha /100 = 0.000474(074) sec - integration time of 3 trasarenu (hexatoms)

The calendar was used in the Vedic world to perform certain rituals and activities.

"Three basic forms of domestic rituals can be identified in simplified form:

Regular sacrifices in the domestic fire based on the Shrauta calendar,
which are less complex than the Shrautas, Samskaras, mostly there are 18 of them,
and rituals of popular culture such as ceremonies and customs, which were formalized in the Grihya-sutras."

"The sacrifices were calendared in relation to the days and the whole year. The sacrificial priest and his wife had to perform at least the daily Agnihotras and the Darsa-purnamasas, in addition to a semi-annual Soma sacrifice and an annual Soma sacrifice as well as vegetation sacrifices depending on the seasons. The priests had to perform these sacrifices for 30 years if they did not die or were too old to perform the sacrifices.

The Vedic calendar is also a highly sophisticated tool for the farmer's planning. It provides vital information about the astrological factors, planets and stellar aspects of our subtle environment that are unseen. With this secret knowledge of planetary and stellar properties, we can understand and analyze how they affect the human mind."

"These effects are real and drastic. We experience the effects of the changes and movements of the celestial bodies due to the gravitational pull of the moon and the sun.

We strongly sense the seasonal changes.
We react to the influence of the massive planet Jupiter as it passes through its 12-year cycle, although we may not take it into account.

Over a dozen factors, each of which moves in cycles through the year, month or day, are identified in the Vedic calendar."