I agree with the other posters but I have seen Southwest delay a flight well in advance - with the same aircraft - over 3 hours for a mechanical problem.
The fix was much sooner and they ended up with a 90 minute delay.
The phone rep said show up for the new departure time. They will not move it up. The airport staff told me that isn't true.
I had the same scenario with American this past weekend in Maui. Already at the airport, one hour prior to departure, they posted a one hour delay for a mechanical problem. It ended up boarding on-time.