First check the label to make sure which medicine is in the medicated feed. Most of the medicated feed we buy in the US is medicated with Amprolium but some, especially certain feeds intended for meat birds, can contain other medicines. Obviously the withdrawal time will depend on which medicine is in the feed.
If the only medicine in the feed is Amprolium, the dosage in medicated feed does not require any withdrawal time for chicken meat or eggs in the US. There is a seven day withdrawal for calves but not for chickens or any other meat animal. Amprolium does its work in the intestines and is not absorbed through the chicken's intestinal walls very well so the dosage in the meat is considered safe.
I'm being careful how I phrase things but as long as the only medicine in that medicated feed is Amprolium I would not hesitate to butcher those chickens. But I would check the label.