It should be determined that the pathogen exists in the operation before you provide an order for antibiotics, but you do not need to wait until a specific colony develops severe visible disease.  Because both bacterial pathogens are highly persistent, a beekeeper who has had issues with EFB in the past, will continue to have problems.  Furthermore, both bacteria cause high rates of inapparent infections, meaning that you would want to treat at the herd level, not just the colonies showing active signs. So, it would be appropriate to provide antibiotics to a beekeeper who has had a history of bacterial disease, even before seeing signs in a particular hive.  This is especially true for EFB, which often shows up in the spring, and you would want to complete the treatment before the honey flow is on.  

I have received this statement directly from the FDA on this topic: 

• Once a veterinarian has determined that American or European foulbrood infection exists within a colony, or group of colonies, whether or not clinical signs are apparent yet, he/she may write a VFD to authorize the use of oxytetracycline for controlling the progression of the disease in that colony, or group of colonies.​

Where I would consider antibiotic provision unnecessary would be the case where a beekeeper has not yet had issues with bacterial disease in their operation (e.g., someone with brand new packages).