I feel like all plants, auto or photo are different, to pin down an exact time isn't truly possible.but you can watch and make sure the tops have swollen, that's a good sign that the window is opening for harvest. If they look all stringy and thin still then you got time to wait, weeks probably. But if you've got bulbous tips and clear color...you'll be ready in days or maybe a week or so at the most I'd say. So just be ready to rock, dont go over feeding and you'll be set.