Opinions will differ but to me that sounds like they suggested to over medicate.
Personally I don't give medicine unless there's a problem (note "medicated" feed I don't consider unnessecary - it's also not laden with antibiotics). Antibs can tax a young chicks immune system. Sure, it might help if they were exposed to filth and sick animals, but prolonged exposure isnt going to help.
I wouldn't be giving it to them for weeks, especially if they're healthy - they need to build their immune systems. Keeping them clean and giving them proper feed and fresh water is key
Welcome! The only reason to give an antibiotic is in the case of an antibiotic responsive illness. If they are healthy, no meds necessary. If they are ill, you don't want them. Stop the antibiotic and see what happens. If they have mycoplasma, for example, they might flair up with sneezing or respiratory signs, not a good thing. I hope your birds are actually healthy and don't need the medication. Amprolium in chick starter is not an antibiotic, and helps with coccidia, so is often a good idea. Mary