Don't do it earlier than 2 weeks. I would say 4, but it depends on how you intend to grow. The fact that your nutrients are geared towards a vegging plant rather than a flowering one means you'll want them to have some extra P and K for when they flower. If you want to flower as soon as it's ready(4 weeks), start feeding at about 2-3 weeks so that it has some P and K built up for flowering. If you intend to veg it for 2-3 months or something, start feeding at 4 weeks. The longer you wait the less chance of nutrient burn... however, if you do wait too long the plant will get stunted and bad growth. Generally, feeding under 2 weeks will be risking nutrient burn. Feeding after 6 weeks means almost definite stunted growth. Obviously, this depends on how much you feed and whether the soil is simple dirt or fertilized. Also if you do intend to start feeding at 2 weeks, use only 1/4 or 1/2 the recommended dosage.