Day and night are designations that a game of Magic: The Gathering can have, which changes the behavior or even the identity of certain cards, particularly those with daybound and nightbound.
Either day or night is first applied to a game when a relevant card is played, and subsequently, the two designations alternate back and forth based on the number of spells cast each turn, or by specific effects.
Day and night were introduced in Innistrad: Midnight Hunt, as a refinement of mechanics which first appeared in Innistrad.
