If I understand you correctly, you are 40 days into flower. If so, your plants look completly normal for many varieties. It is very common for leaves to yellow during this time. It is the plants last effort to put every bit of energy it has into making the buds. That's it's lifes goal, so it is actually eating parts of itself that are not as important as the buds are. There is nothing you can do about it.

And welcome.