If they are coming, it will take about 30mins. Far too quick for a headline to make the rounds. What you might notice (depending on if your country thinks it u

If they are coming, it will take about 30mins. Far too quick for a headline to make the rounds. What you might notice (depending on if your country thinks it useful) will be siren signals and radio/TV broadcasts. But I guess it is even too short a time for those, and you cannot do more than "move into the cellar" anyways.