@NORBY, I did something similar by going from 24/0 down to 19/5. I just did it in small steps going down 15 minutes at a time. Didn't see any adverse effects. I did 24/0 through veg to see if it would make a difference. Believe it did as the plants seemed to be a little bit larger, but no definitive proof.
Now I split the difference and do 19/5. The most common schedules are 20/4 and 18/6.
I cycle my lights at 20/4 because after trial and error it seemed to consistently produce the best results. But at the end of the day, proper DLI is the key no matter the schedule.
My set up is very different than anyone elses, I can set GPS coordinates, I use a lat of 66*N. And the first day of the plant above soil I set the date as May15th thru June 1st. The controller then sets sunrise/sunset for each day to match that locations actual sunrise sunset.In the Olden Days...cough...cough......Breeders would stick Autos up to Sex on 18/6....then change them to 24 hour light.....and that would Flush out any Hermies...........
Yes, still trimming, and yes, the new grow room really has delivered.You Finished with Trim jail @MedCzech .....?........has the New growroom paid you back for all the hard work......?
Back on the music subject little stranger is one of my favorite LS artist finds thanks @Frank the Dank and @PinkyNotTheBrain