Light cycle

** i say 12 hours as a comparison.. obviously you don't want that in vegetative period with photoperiods growing or for autoflowers, since it's highly unlikely to be more efficient at that power compared to over 18-24 hours.

if you have a really weak light, 24 hours is what you want. Read up on DLI. Other factors - CO2? use your specs from light to determine how many hours of light you can give it (with or without CO2 pumped in). Giving it more light does not help and will in fact hurt the plant. It can only metabolize so much, so fast given the environment it is in - mainly CO2, but temp and humidity will impact how much light it can use per 24hours too. There's a nice DLI chart out there. Bet google image search shows it near top. e.g. 12 hours/day at 900par (that's specific to m^2), is the upper limit without CO2. To get that DLI with 50% more hours of light, you can reach the same DLI with 18hours of 600PAR light. (directly proportional) so, it depends. If you got umol/s you can apply that to your footprint and proportional to what that would be in 1m^2 to determine your par for your area. A little algebra goes a long way, here. then use the chart or the above ratios will guide you too.

I've been going 18/6, but since it's still in the ground, I'd through a humidity dome or a ziplock back over to contain humidity over the seedling. AFAIK, the light doesn't matter now until the seedling pops through. I'm only on my first grow so I'm not well experienced, but have read both 24/0 and 18/6, though a lot of people leaned toward some darkness. PS. This is the only thing keeping me sane since hockey was cancelled, I wanted to see some playoff McDavid