When to add nutes

so im using happy frog soil and i also have fox farms nutes. my question is how long will the nutes in the soil last before i should start adding nutes? my plants are almost 3 weeks old.

anybody have any suggestions?

I am not a soil guy and I guess the frog is happy because it is fortified soil?I figure start out with 1/8 strength ph balanced nute solution between waterings and work up from there.If plant gets burned flush with ph balanced water and note at what strength she burned and back off.make sure you have a dry out period(not bone dry) between water/nute feedings.
Did I mention I am not a soil guy?