Put it on 24 hrs a day to help keep things warm and to aid in drying out the soil for you. Temp fluctuations aren't something seedlings particularly like. Also, as far as watering goes, you need to let it get VERY dry. If you want a good healthy root system, refrain from watering it so those roots branch out and search for moisture. When the very top of the cups soil gets dry and crispy, but it's still got a little weight to it, it's almost ready. You really have to go by the weight of the cup. When it starts lightening up, it's time to add A bit of water. And DO NOT SOAK IT! Just add enough to where it doesn't even come out of the bottom holes.
One of the most common mistakes newer growers make is excessively over watering their seedlings because it's "Fun" to tend to their plants. Don't be that guy.