Historical Rules · 19 November 2021
Rule 502.2
Official source text from the 19 November 2021 Rules release
Second, if it’s day and the previous turn’s active player didn’t cast any spells during that turn, it becomes night. If it’s night and the previous turn’s active player cast two or more spells during that turn, it becomes day. If it’s neither day nor night, this check doesn’t happen and it remains neither. This turn-based action doesn’t use the stack. See rule 724, “Day and Night.”