You do not require any light for germinating/sprouting. I attached a picture of 2 plants I currently have going. It took about 4 days to grow a 1/2inch taproot on her, I kept them well watered, in 3 more days I had 2 sprouts showing. They are now under light and flourishing beautifuly.

So to answer your question, after the taproot has shown, and you plant in soil, it should take about 2-10days. Anymore time than that and it is a good chance she won't pop. Keep the soil moist at all times while she is still sprouting. Don't let that freshly sprouted root dry out in the soil, or it will die. When it has finally sprouted, then start going through the wet/dry cycle. Good luck, peace.