Light setting change this late?

I believe that you should stay with the 18/6 schedule since it gives more than the usual 12 hours of light during flowering, plus the plant needs hours of darkness to actually burn and use the sugars and proteins produced by photosynthesis during the day - this promotes new vigorous growth. You could try 20/4 light schedule but with care! that may cause radiation/light stress and will inhibit growth! Anyway switching the light schedule at this point wont harm your plants as long as you give it enough hours of light (over 12 hours at this point) and dark (4-6 hours at this point). Hope this helps! Good luck and happy growing :)

I did 18/6 on my autos and they grew beautifully. Check my completed diary, I got 20oz on 3 plants in a 4x4 space.

Technically there should be no issue to doing this. Thou I'm a firm believer they grow better with some rest. 🤘😤