You could start using nutes now for plant in pic 1 and 4, I would give the ones in pic 2 and 3 a week or so more. Start with weak solution fist, about 1/4 recommended strength, if the plant reacts well then you can slowly increase the dosage of the next few week.
As for the bulb, put your hand at the top of the plant and lower the light to the point you can hold you hand under it without your hand getting hot.