They get nutes when they hav a developed root system but depending on the set up u might not be able to c the roots good rule of thumb is after the 3rd set of leafs are visable I would start to slowly and nutes
most soils have nutes for atleast 2 weeks. i use terra canna plus and it has nutes for 2 weeks. i now use terraveg nutes and switching to terra flower.
very vague, you shouldnt be giving any nutes to seedlings if you have a good mix of soil... I personally dont start feeding until the second week after hairs show in flowering.
good advice if he doing a sog in soil
but is he ??
they could be in rockwall just rooted to go into hydro system
that's find out what he is doing first
and his set up