Soon my friend very soon, if u want to go full strength go for it, like u said best idea is to clean out the res again and start with fresh water and go full stength, top off the res every day if u can for a week and start over, try and put a water line in the bucket if u can, DWC's loose water pretty quickly, and the nutrients become more concentrated. It looks like your plant is getting some good growth so i def. exaggerated on the 3 week finish time. Keep an eye on the tri's, when u see amber its a good indication harvest time is prime, but u can wait until there all amber and u will get the most yeild, i would do 50/50 couldy/amber. When u start to see 25/75 flush the plant with distilled or normal water no nutes, u will get a nice clean smoke.