If you want high, not sleepy, harvest asap.
18/6 is far better for your plants, I am amazed they have survived this long without sleep.
Would love to try some and see how affected the trichomes are due to your plants not having a normal metabolism or photosynthetic routine.
Just remember, everything on planet Earth has evolved with sleep, this includes cannabis too.
Unfortunately your plants have missed out on 20 weeks of a normal metabolism and I wonder how this has affected the trichome composition.
Without a sleep every night, your plants have missed out on undertaking certain vital metabolic processes that they can not do when the lights are on, leading to an incredibly unbalanced metabolism.
If you are keen, google "photosynthesis" and find out why sleep is vital for proper plant functioning.
Hope this helps, Organoman.