I totally agree with Ken. You want them to GROW to their potential. What are your goals? Do you plan to breed them at 14-16 months old? (recommended) They need to be in good BCS at that time so that they have been cycling for a couple of months.
I wean my calves in the fall and we have brutal winters. They are NOT indoors or have woods to get into. I feed excellent baleage and 5#/hd/day of whole shell corn.
"IF" your grass is good "growing" grass (not old headed out) and you rotational graze, they will probably have adequate feed with loose minerals 24/7.
You have not filled in your location, so we don't know where you are located. Location dictates what program works. Here in Upstate NY, if you rotational graze, we have excellent feed quality all summer into fall until the snow covers it.