As with any X vs Y weapon, the scenario matters a whole lot. If you know where the missile is going and your interceptors are launched from that area you have

As with any X vs Y weapon, the scenario matters a whole lot. If you know where the missile is going and your interceptors are launched from that area you have plenty of time. This is the situation the USN is looking at with the new Chinese anti-ship ballistic missiles. On the other hand, a system to protect the continental United States from incoming missiles from anywhere to anywhere was always fanciful.