A poetic way of appreciating the vastness of time....
The Shiva Puranas were first written down in 4-6th century, but are said to have been orally transmitted since ancient times. (There are some references in older Upanishads from 5 th century BC to the Puranas for example.)
But anyhow....this can be read like a poem, even if the words are not understood.
The basic unit of life is nimesha, the instant.
Fifteen nimeshas make one kastha, thirty kasthas one kaala, thirty kaalas one muhurta and thirty muhurtas one day.
Thirty days is a maasa, a month, which is one day of the gods and ancestors;
six maasas make an ayana,
two ayanas a year.
One human year is a day and a night.
Three hundred and sixty-five human years make a divine one.
Four are the yugas in the land of Bharata: the krita, treta, dwapara and kali.
The pristine krita lasts 4,800 divine years, the less perfect treta 3,600 years, the half-corrupt dwapara 2,400 and the almost entirely evil kali, 1,200.
A chaturyuga, one cycle of four ages, is 12,000 godly years long, 12,000 X 365 human years.
Seventy-one chaturyugas make a manvantara,
fourteen manvantaras make a kalpa.
A kalpa, of 1000 chaturyugas, 12 million divine years, is one day of Brahma, the Creator.
8,000 years of Brahma make one Brahma yuga;
1,000 Brahma yugas make a savana.
Each Brahma lives for 3,003 savanas.
One day of Vishnu is the lifetime of Brahma.
One day of Shiva is the lifetime of Vishnu.