Large NEOs are very unlikely at this point for the reasons you've given. It's advanced warning on anything else that's needed. Redirection is another topic, but we have no experience and only theory on the best ways to do it, and wouldn't know which technique to try before a close examination (which means time to find it and get to it just to figure that out). As for advanced warning for evacuation, that's probably the most likely scenario, but it's also morbidly funny to mention in a thread discussing near misses found days before its passing, and often we see articles about the rock after the fact. (Although maybe it was known about before by experts, just didn't hit the press in time)