First of all, glad you could save this bird.

I have no clue how often baby robins should be fed, but I believe it also depends on its age. You can get a handfeeding kit for baby parrots at most pet stores. Perhaps, if you ask them, they may have one for wild baby birds too. I know that baby parrots need to be fed every 2 hours until they are weaned (yes, even at night), so I would assume its the same with the robin. Good luck and let us know how it goes!