It depends on if they're still getting milk, what your pasture quality is (if they are on pasture) and on their health.
If they were healthy from the beginning, with no cocci problems, other parasites, illness, scours, etc. and they got enough milk and creep food then keeping them on a small ration of grain along with plenty of hay should be good as they come off milk. If they are still getting milk I wouldn't give any grain unless its in small amounts for bribe/treat for training. If your pasture is pretty lush and has lots of forage then giving a small amount of hay once or twice a day to establish a feeding pattern might be all that's needed. When they're growing I want to make sure they always have something to eat. A good, leafy hay is good for establishing their rumen.
If they've been sick and are underweight you might continue them on milk or replacer, and supplement with more grain as well as free feeding the hay. The grain tends to be higher protein, higher fat and higher sugar. Also higher phosphate so consider Ammon.chloride if you use much grain in the diet.
Its never too soon to start with loose minerals either.
We still have them on a at least 1xday bottle feeding at that age, plus free choice alfalfa hay (or good quality grass hay and alfalfa pellets, both free choice), and grain 2x daily. Minerals free choice.