Just Transplanted, how long til i should start feeding nutrients???

Quick question guys. have a couple clones that have rooted and just been transplanted into 1 gallon pots. How long should i wait to start giving them nutes. the soil i used for the transplant is some 2nd year organic mix( it was free but not exactly sure what it is) and i have added some worm castings as well as kelp meal when preparing the soil. also one last question, can too much iron in water be a bad thing? thanks

not too sure about an abundance of iron being of any effect. im interested to see if anyone knows. anyways i like to start at a low 250 ppm as soon as they root then when i go to first transplant ill up it to around 600. 900 parts feeding after i top them and full nutes after a couple inches of response. i dunno what most people are doing here at all honestly. ive tried a few other time frames over the past few years that were recomended but when i started applying the techniques i currently use and really paying attention easing them in somewhat early def promoted the best health. although ill probably be making 3 transitions next time. my girls are pretty hardy strain so that helps too