I friend has some seedlings growing in jiffy plugs under CFLs and they are almost two weeks old. Could they be fertilized yet?
You can start at 1/4 strength at every other feeding and slowly move up from there, flushing every 2 weeks. Just be careful cause its a young plant.
Like I said, every other watering. So if you water every 3 days you could go 1/4 first water after 3 days use just plain water then after 3 days nutes at a diluted amounts etc etc etc. If you see signs of nute burn stop feeding and flush. Thats how I start introducing nutes to young plants. Be careful with liquid food, as this is very concrated and strong.