You want to feed the feed with amprolium until your chicks have been out on your ground for a couple of weeks. It's meant to help them develop some immunity to an overwhelming load of coccidia in the soil, so stopping the diet before soil exposure does nothing for them.
Most small flock owners who don't take their birds to poultry shows leave out almost all the possible vaccines available.
The exceptions are Marek's vaccine, given at the hatchery to day old chicks, if you order it, and the coccidiosis 'vaccine', which is a low dose of a less aggressive strain of coccidia, meant to help them too. I have my chicks from hatcheries vaccinated against Marek's disease, and skip the other.
One feeding of amprolium treated feed wipes out the coccidiosis 'vaccine' and IMO it's not worth the money.
Some flocks will have bad problems with coccidiosis, unless the chicks get medicated feed. Other flocks never have issues, although that could change any given year, depending on soil conditions.
Mary