Most airlines tell you to arrive at the airport 2 hours prior to departure and for many airports, that is sound advice. As for our airport here in Billings, I had gotten a little spoiled - showing up only 45 minutes before departure and still spending 30 minutes of that waiting at the gate.
I'm not sure how far down into town the alarms will make it, but if you know someone who lives near the airport you might want to let them know...or be mean and tell them there is a conflict with North Korea and to take shelter if they hear an alarm.