sahasra-yuga-paryantam ahar yad brahmaṇo viduḥ
rātriṁ yuga-sahasrāntāṁ te ’ho-rātra-vido janāḥ||17|| 

Meaning : People who understand the truth know that one day of Brahma lasts for a thousand yugas, and his night also lasts for a thousand yugas. A day of Brahma (the creator) lasts for 1,000 yugas, and his night is equally long. Those who understand this know the vast scale of cosmic time.1,000 yugas = 1 day of Brahma = approx. 4.32 billion years
So 1 full day and night = 8.64 billion years