If it becomes day or night or if a
daybound (If a player casts no spells during their own turn, it becomes night next turn.) permanent enters, track day/night for the rest of the game.
As it becomes day, transform all
nightbound (If a player casts at least two spells during their own turn, it becomes day next turn.) permanents.
If a player casts no spells during their own turn, it becomes night next turn.