Analysis of information sources in references of the Wikipedia article "Saptarshi" in English language version.
a day in the life of Brahma is divided into 14 periods called manvantaras ("Manu intervals"), each of which lasts for 306,720,000 years. In every second cycle [(new kalpa after pralaya)] the world is recreated, and a new Manu appears to become the father of the next human race. The present age is considered to be the seventh Manu cycle.
In each Manvantara (period of a Manu), seven Rishis, certain deities, an Indra and a Manu, and the kings, his sons, are created and perish.
Paraphrased: Mahayuga equals 12,000 Deva (divine) years (4,320,000 solar years). Manvantara equals 71 Mahayugas (306,720,000 solar years). Kalpa (day of Brahma) equals an Adi Sandhya, 14 Manvantaras, and 14 Sandhya Kalas, where 1st Manvantara preceded by Adi Sandhya and each Manvantara followed by Sandhya Kala, each Sandhya lasting same duration as Satya yuga (1,728,000 solar years), during which the entire earth is submerged in water. Day of Brahma equals 1,000 Mahayugas, the same length for a night of Brahma (Bhagavad-gita 8.17). Brahma lifespan (311.04 trillion solar years) equals 100 360-day years, each 12 months. Parardha is 50 Brahma years and we are in the 2nd half of his life. After 100 years of Brahma, the universe starts with a new Brahma. We are currently in the 28th Kali yuga of the first day of the 51st year of the second Parardha in the reign of the 7th (Vaivasvata) Manu.
Each manvantara is preceded and followed by a period of 1,728,000 (= 4K) years when the entire earthly universe (bhu-loka) will submerge under water. The period of this deluge is known as manvantara-sandhya (sandhya meaning, twilight).
