Comprehensive Rules
502.2
Second, if itâs day and the previous turnâs active player didnât cast any spells during that turn, it becomes night. If itâs night and the previous turnâs active player cast two or more spells during that turn, it becomes day. If itâs neither day nor night, this check doesnât happen and it remains neither. This turn-based action doesnât use the stack. See rule 727, âDay and Night.â