When to fertilize?

When does a seedling (from seed) need fertilizer?

If I use a soil-less mix like pro-mix, which has no nutrients and my water has little or nothing in it, the seed sprouts, seedling with two leaves appears, when do I need to start feeding it?

After the next (true?) set of leaves appears? Before that?

I know it will be a low dose, but just not sure when to start feeding?

dont start feeding until you start flowering

If there are no nutrients present in the soil, I start feeding at 1/4th strength after 2 weeks from sprout. Anything before I just use plain water.

yea just add water until you get a good established root system..until then u can give it something like Superthrive