This type of warning "in-bound missiles" are extremely time sensitive. Yes, we can expect that the National Warning System (NAWAS) ring-down system could provide a voice warning. But you cannot expect states and especially local jurisdictions to be able to turn that warning around and issue "timely" warnings to their respective populations. Do you think a 911 Center Manager could on their own turn that warning around effectively and efficiently at 2 a.m.? Not in my world!
The majority of all local emergency management agencies are not 24/7. They have specific "duty officers" who take a duty book home, and they do not have any specialized communications equipment. The best tool available nationally is the Emergency Alert System (EAS), which at the presidential level requires all broadcasters to carry a national level message. No national EAS has ever been done to my recollection. 9/11 would have been a good time to use it in my opinion.
The only way an "accurate and timely" warning could be issued is at the national level by national command centers with permanent 24/7/365 staffing. To think otherwise is simply crazy thinking and comes from someone trying to avoid the responsibility of their duty.