Just watch the cotyledons.
Them round ones.
When they start to shrivel and yellow, it's time to start light feeding.
Very light, at first.
If you watch closely you can keep the cotyledons green and healthy looking right up to flowering.

When they pop their 3rd set of serrated leaf, go ahead and call them seedlings.
By the 6th set, I call mine saplings.
They thrive on flattery.

Call them Ishmael, if you wish!
It no matter.
Point is; Every plant is a little different.
They do try to tell us what they need, and we eventually learn to read them.

Aloha,

Weeze