When should i start cut down on nutrient solution ...

Dark green leaves are a sign of nitrogen toxicity; and it has many drawbacks: including nutrient lockout, weak stems, reduced yield for starters. So you should reduce the feeding already and let the plant consume it's reserves. I strongly advice you to get an EC/PPM meter, it will allow you to stop guessing how much to feed. Anyway, give plain water for now until the leaves are a more healthy light green. As stopping feeding at the end of the grow; once the buds stop fattening, you stop feeding, that will give you 10 to 14 days for the calyxes to swell and thricomes to mature.