Yellow leaves are increasing, so harvest time is getting close. Now is time to stop feeding and start flushing all the nutrients. I'm going to do one more week of only water and then i would harvest.
I would say you have at least a week most likely two though. I would invest is a little Carson microscope from Amazon. The blue one work great and is around 10-15usd. That is the only real way to be sure. Looking good and happy growing!!!