If you're using soil, and it's not shit soil. You likely won't have to feed until a couple of weeks iinto flower.
- If shit soil, then when the first two tiny leaves that it sprouts with, starts dying off, that's when you start feeding. They're a nutrient bank for the seedling.
If soiless grow medium, you're gonna have to start early, as it don't have any nutrients to grow in. .. But I don't have any experience with that, so can't help you there.