You can feed them any time you want. When they are first born, you don't have to worry about feeding them right away because they are still absorbing yolk. Sometimes, you can even see a lump in them where it is being absorbed. That being said...I offered rat pups, and most of my babies ate, the day after they came out of the egg. The ones that don't eat rat pups will usually chow down on a mouse. It will be easier though, in the long run, if you can start them on rats.
They will go through a shed about 7-10 days after they hatch, regardless of whether you feed them or not. However, for the most part, they should not hesitate to eat almost immediately.
Good Luck.
Tom