I don't know that they are required to respond at all. The EEOC is an investigative organization that can file a lawsuit against a company if their investigation finds that the company illegally discriminated. They don't have the authority to actually punish a company for anything themselves, they have to ask a judge to do so. The EEOC themselves would be in a better position to tell you when they will go ahead and make a decision without input from the company if the company chooses not to respond.