depending on what medium you'll be growing in (I recommend rockwool for seedling) you should put it in the growing medium as soon as the sprout comes out of the see. then you should keep it in the dark in a humid/warm environment until it comes above ground. I keep my rockwool cubes on a heating mat with a humidity dome with the temp around 78F and the humidity around 80%. Once they come above ground, you should put them under fluorescent light (if available) and remove the humidity dome. if you dont have a dome, you can poke a hole or 2 in a ziplock and surround it over your cube until it comes above ground.