wait until the cotyledons fall off before you add nutes, do one shot with bloom nute as they make your roots explode then go with the veggie nutes till flower, usually 3wks but I'm not a hydro grower so maybe you start sooner.
in hydro you need to feed from the start with a very low dose and build up to the max dosage.
I fertilize my coco\perlite plants from their first watering after being planted with 1\3 strenght.