You can use the ACV right now if you want to. A tablespoon to a gallon of water or proportional fraction thereof. I've used it and not used it with various batches of chicks and could not tell any difference one way or the other.
Chick grit is only necessary if you''re feeding something other than finely ground chick starter. Ordinary mash feeds do not need grit. I personally don't feed anything that might need grit before one week of age. After that I feed finely chopped green feed in small amounts. I just sprinkle the grit over it like salting food.