I wouldnt feed them but Im not as pro as rzza but I think they should start going soon, 3 days is nothing it can happen, they could be working on roots - just make sure your enviroment is favorable - Seedlings like high humidity and a good temp around 78F give or take 5 degrees either way, many growers use something to keep their seeds about 80F if they are getting to cold it WILL slow things down, it has been kind of cold the past few days I guees so this could be the reason. Good air exchange is important also, It is said that the seedlings have enough food to last them for 2 weeks so feeding I think is unessecary, you could try a little vitiman B like some superthrive with the next watering.
My opinion is wait till they lose the cotlydens before feed them, this is the sign they have graduated seedling stage and plants are supposed to have enough food natrually to get thru the seedling stage.