Not long. People will tell you that nitrogen is bad in flowering, but thats pretty much nonsense. lol. It's true the plant will be increasing its uptake of p and k, but n is still important. You want your fan leaves to be as big and healthy and around making the buds lots of energy for as long as possible. During stretch phase of flower when it uses a ton of nitrogen i give my plants veg nutes every 2 feedings. In the budding stage of flowering its probably about 1 every 5 feedings.