TornadoADV said:
More like 30 minutes for the ICBMs, 5 to 10 minutes from the SLBMs if they've managed to move next to our coast.
That might mean 4 minutes of early warning before the missiles in flight reach their targets.
But anyway, the time between the flash and the heat reaching you might be enough warning for you to survive, same with the blast. In Japan, people would see a bright glow in the air, and go to the windows to see what was going on. The blast hits the windows, and they get a face full of broken glass. I think much the same happened with the meteors in Russia.
Just telling people not to do that would save lives. Telling people to duck and cover would save more.