According to what I've found so far, robins need feeding every 15-20 minutes, dawn to dusk. Oof. CuriosityCat is also correct, in that the parents add in a lot of things while the grub's in their crop- but I think it may be possible to synthesize this with some sort of parrot formula or added...
You'll be in for a lot more work if you hatch them as opposed to chicken eggs. You do have to hand feed several times daily and you can't feed them chick starter unfortunately. You may be able to pick up some parrot formula from a local pet store, though, and that may work. If you're willing to...