While the 1 hour rule is mostly true be careful with discount airlines. Frontier Airlines does do a 1 hour boarding. I've heard of cases that if you are late to boarding, even if half hour ahead of departure, they will not let you board the plane. I'm sure it depends on specific airport agents protocols. My point is I'm not sure you can always use the 1 hour buffer.

I was definitely stopped from boarding when I arrived to the airport 45 minutes before departure when on Spirit. That was the last time I used Spirit.