About two weeks after they pop thru the soil. Start with a weak solution, only 1/4 recommended strength and then slowly build up with subsequent feedings.
Yes, earth juice is a good brand. As for when to start nutes. I typically wait until the round starter leaves are just about dried up. (the two little round leaves at the base of the plant). This means that the plant has used all of its stored nutrients. And, like toasty said. Start off with a weak solution. Better to underfeed them at the early stages than over feed them.