The lines in T1 (for Southwest and US Air) can be very long. I really despise going through that terminal. It also seems like everyone is pretty slow there at getting through security. I think 2:20 is going to be tight from an international arrival, unless you have Global Entry and don't have checked-in luggage. If you're not a US citizen, the lines can be pretty long for customs and immigration in TBIT.

The good thing about Southwest tickets is, you can cancel them and not have to pay a fee. The value will just be held for future travel. If you can find a decently priced later flight, I'd do that instead so you wouldn't worry; it is a vacation after all, no?