afaik, you shouldn't need to use nutes untill about 2-3 weeks... the seedlings will be drawing their nutes from the seed leaves. this should be enough to get them through this time. I would start to use nutes when these seed leaves start to turn yellow, as this is a sign that they're close to being used up. and as stated above, you want to start at 1/4 strength, and work your way up.