te janāḥ (ye)–Those who; viduḥ–know; brahmanaḥ–Lord Brahmā’s; ahaḥ–day; yat–which; sahasra-yuga-paryantam–comprises the duration of one thousand chatur-yugas; rātrim–and (his) night; yuga-sahasra-antām–of the duration of one thousand chatur-yugas; ahaḥrātra-vidaḥ–are knowers of day and night. [17]

A day of Lord Brahmā lasts for one thousand chatur-yugas*, and his night is of the same duration.Persons who know this have the true conception of day and night.* One yuga (age) in the time calculation of the demigods equals the four yugas or one chatur-yuga in the time calculation of man, or 4,320,000 years.