Autoflower drooping at night

18/6 is optimum. Plants are most probably exhausted/stressed by doing 20/4. Some plants will droop before "sleepy" time, but if everything is ok, they should generally hold their leaves up until "sleepy" time. Your plants will grow just as fast and possibly yield more at 18/6 due to being healthier with the optimum light/dark ratio that 18/6 provides. Cannabis can only grow so much during any 24 hour period and this growth tops out at about 18 hours, meaning running your lights longer than 18 hours, is basically a waste of electricity. Cannabis also needs to "sleep" and undertake certain metabolic processes during the night and 4 hours is probably not quite enough time to do theses processes, taxing and stressing your plant. You will not lose anything by going to 18/6, in fact you will probably gain much by having a healthier and happier plant. Plants are not machines to be pushed to their limit, they require a proper cycle of awake/sleep/awake/sleep, and this has been proven through 80+ years of research into cannabis, to be 18/6, for optimum growth and optimum health. Despite what you may have read or been told, 18/6 is the best lighting schedule for autos or photoperiod plants in vegetative growth. Besides, if you can get as good or better results by running your lights 2 hours less each day, this will add up to a nice saving on your electricity bill over a typical 12-14 week grow cycle. Hope this helps,........ Organoman.