Twelve hours dark causes the plant to flower. We call it the flip to flower. Most common veg light cycle is 18h on 6h off. No nutes until after two weeks or the cotyledons turn yellow. That's the first two round leaves the plant pops with. I assume you're doing hydro?
No I'd say two weeks from now you can feed at 1/4 strength for the first time. Fill that net pot up too, you don't want light getting into the reservoir it will cause root rot and slime buildup. You want to start nutes when she looks more like this: