Shoot on southwest you shouldn't have a problem. Just don't stop to gawk around. I buzz through that airport with a 45 minute layover anytime i head to Orlando. Now i usually fly Delta which makes up the majority of the Atlanta airport and I usually have to take the little monorail from one end of the airport to the other, but Southwest is isolated to a pretty small area in the airport, you shouldn't have a problem.
Remember you don't have to be there when they start boarding, you just have to be there before they close the doors.