ahar yad brahmano viduh
te’ ho-ratra-vido janah
(Attaining the Supreme ,Text 17, Chapter 8)
Meaning: By human calculation, a thousand ages taken together form the duration of Brahma’s one day. And such also is the duration of his night.
****The duration of the material universe is limited. By calculations the life of Brahma seems fantastic and interminable, but from the viewpoint of eternity it is as brief as a lighting flash. In the material universe not even Brahma is free from the process of birth, old age, disease and death.
Bhagavad Gita: The duration of the material universe is limited (Attaining the Supreme,Text 17, Chapter 8)