vedic timekeeping

The Hindu metrics of time can be summarized as below. Hindu ''Kaala Vyavahara'' (Metrics of Time)

Sidereal metrics

a paramanu is the normal interval of blinking in humans, or approximately 4 seconds
a vighati is 6 paramaanus, or approximately 24 seconds
a ghati is 60 vighatis, or approximately 24 minutes
a muhurta is equal to 2 ghadiyas, or approximately 48 minutes
a nakshatra ahoratram or sidereal day is exactly equal to 30 muhurtas (Note: A day is considered to begin and end at sunrise, not midnight.)

A leekshaka is 1/60th of a pranamu, or 1/15th of a second;
a lava is 1/60th of a leekshakamu, or 1/900th of a second;
a renu is 1/60th of a lavamu, or 1/54,000th of a second;
a truti is 1/60th of a renuvu, or the time it takes for a needle to penetrate a lotus leaf, or 1/3,240,000th of a second.

a Tithi (also spelled thithi) or lunar day is defined as the time it takes for the longitudinal angle between the moon and the sun to increase by 12degree. Tithis begin at varying times of day and vary in duration from approximately 19 to approximately 26 hours.
a paksa or lunar fortnight consists of 15 Tithis
a masa or lunar month (approximately 29.5 days) is divided into 2 pakshas: the one between new moon and full moon is called gaura (bright) or shukla paksha; the one between full moon and new moon krishna (dark) paksha
2 lunar months are 1 Ruthu
3 Rithus are 1 Aayanam
2 Aayanas are 1 year

a yaama is 7½ Ghatis
8 yaamas 1 half of the day(either day or night)
an ahoratram is a tropical day (Note: A day is considered to begin and end at sunrise, not midnight.)

Years are grouped into yugas (ages):

One cycle of the above four yugas is one mahayuga (4.32 million solar years)
A manvantara consists of 71 mahayugas (306,720,000 solar years)
After each manvantara follows one Sandhi Kala of the same duration as a Krita Yuga (1,728,000 solar years). (It is said that during a Sandhi Kala, the entire earth is submerged in water.)
A kalpa consists of a period of 1,728,000 solar years called Adi Sandhi, followed by 14 manvantaras and Sandhi Kalas for a total of 1000 mahayugas or 4,320,000,000 (4.32 billion) solar years.
Two kalpas constitue a day and night of Brahma; the life cycle of Brahma is one hundred years of Brahma, or 311 trillion years.

The current Kali Yuga (Iron Age) began at midnight 17 February / 18 February in 3102 BC in the proleptic Julian calendar.