I applied online. The process took 3 months. I interviewed at Southwest Airlines (Dallas, TX) in Feb 2019
Interview
Applied online in October. Landed a phone interview about two months later. They flew me out to their headquarters for a final round in February. Overall the process was very laid back and they were helpful along the way.
I applied through college or university. The process took 4 months. I interviewed at Southwest Airlines (Dallas, TX) in Jan 2016
Interview
Fairly easy: resume screening, phone interview, in-person interview (Dallas HQ). Each interview was about 30 minutes, with the recruiter being a part of both interviews. Simple questions were asked, nothing too complex, but it depends on your recruiter.