Those who know the day of Brahman as a thousand cycles of ages (yugas), and his night as a thousand cycles of ages — they are knowers of day and night.

Cosmic scale: one “day” (ahaḥ) of Brahmā = 1000 mahā-yuga (cycles of 4 yugas). One “night” (rātri) likewise. During the day, manifestation; during the night, partial dissolution.

Aho-rātra-vidaḥ — those who know this understand cosmic time. It is perspective to understand that even Brahmā is in samsāra.