Approximately 4th century. Much earlier than that, only among Gnostics.
Ah, let me see if I understand your view here. The entire orthodox Christian world knew nothing of the veneration of Mary.
Then in the 4th century, the entire ancient Church from India to Africa to Gaul suddenly realized "Golly gee! The Gnostics must be right!" and flipped over like a light switch.
And no one objected to this? Not one voice was raised against it? And just this *one* tenet of gnosticism was adopted, while the rest was despised as a heretical abomination from the pit of hell?