You're going to need to provide the info on this - what are you lows at outside? What are your current brooder temps at (high and low)? Have you begun weaning them off heat at all?Do they still need the heat lamp?
When can they go outside?
I give my chicks grit from the start. As far as when they "must" have it, by the time they go outside or are given anything other than milled feed to eat (i.e. treats).At what age do they start needing grit?