If the leaves start to turn a paler green or yellow green during veg, it’s time to feed. Yes Ok to feed after 6 weeks if the plant needs it. Best to look at plant to make the decision to fertilize, not the number of weeks. If the plant looks like it is getting ready to be harvested in 2-3 weeks, Based on the development of the buds, then you can cut back on nutes. When you get to that stage post pics to get more advice OK?