When the roots start showing through the sides or bottom of the peat puck, ok to transplant.

18 to 24 hours of light, but on a steady schedule. Don't switch back-n-forth. I use 18/6 from seedling to flower, but some don't.

Do not let the seedling dry-out, but don't let it sit in water, either. A happy in-between will do. Don't forget 'em. They dry quickly.