with your flight on southwest coming in have you looked for the prior routes that flight is on that day. If this is a flight coming from a hub airport and it’s incoming us delayed then they could substitute the plane/ crew being on time. If this coming on a different route eherr it’s going through a non major hub could see delay like a SJC to LAX. Many of the western routes can be separate where they fly NW-bay area/ SMF/Reno to LA area/ SAN are run back and forth but then they will occasionally throw in a flight from denver/ Midwest into one of those cities then it enters the west loops.