The White OG

Easy way: ON/OFF in hours 24/0 to 18/6 for seedlings 20/4 to 18/6 for vegging and flower Some users grow autos under 24/0 all its life, but plants need rest. the down time can help them a lot. I grow in 18/6 for the plants entire life, can go lower to save on hydro as well. even seen 12/12 from seed on autos but they do get a bit stunted in growth. Good Luck!

my simple tactics in mass grows was to keep 24/7 for first 7 days, since seed breaks soil, unless i see big inter nod stretching, then i switch for 18/6 for all veg, when i am happy with size, i change to 12/12 for photo-periods.

Read up on DLI. You'll see it makes very little difference if oyu use a 16/8 vs 20/4 as long as you provide same amount of DLI. If lights are a bit lacking, that is the only time you will benefit from using longer days like 20/4 or even 24/0. Having a dark period is best, but in an extreme situation with shit lights, it might be beneficial to go 24hours. reducing an hour is sometimes just easier than fiddling with a dial or messing with height from canopy. I prefer my height from canopy to set optimal area of coverage -- the geometry of it and distribution of light being the most important factor later on in bloom. In vege i don't mind using height as a dial, though.