First

First of all, what you have there is a soil less grow, not hydro and not soil. When growing in coco (or coco with perlite), you need to water / feed every day and let some run off to wash excess salts. Second, you never let coco dry out. Third, when using coco you need to use cal mag from the beginning, else you get deficiencies like you have now. Fourth, you also have some potassium deficiencies there (K), that needs to be solved.

Wait till the plant stops growing lots of new bud and new white pistils, eventually more will start turning red and receding than there will be new white ones are sprouting and growing. Now the bud is starting to mature. When it looks really swollen everywhere and almost all red hairs have receded and almost every calyx is swollen even the newly formed ones it is probably a good time to harvest. Harvest up to one or two weeks from this point. Easier to watch a plant flower over time to see how it is maturing rather than just look at the buds and say its done. Fruit and veg is exactly the same, should be able to see it change and swell as it matures, when it looks like it has matured and swollen enough and taken on mature colors you know its good!