Probably won't be long till they'll be chomping on it. at 4 days thats still pretty young for catching on to what to eat. They'll get the hang of it soon.
As above but as they get towards the end of the first week they'll really start to pull away. Just keep offering chopped greens for now. Ours all differ and some seem to prefer starter crumbs while others prefer the chopped greens. By the end of the first week they're all taking both and out in grazing pens for a few hours when the weather permits.