https://abukhadeejah.com/the-mention-of-the-takbir-is-legislated-from-sunset-on-the-night-before-the-1st-day-of-dhul-hijjah-by-shaikh-khalid-ibn-dahwi-adh-dhafiri/
The Takbīrs are legislated from sunset on the night before the 1st day of Dhul-Hijjah ― Shaikh Khālid Ibn Dahwī Adh-Dhafīrī