I got Lois out of bed and dressed, loaded her into the car, checked the online flight status one last time (no change), and headed off to the airport to meet the flight which was rescheduled to 11:43pm. We were only a couple blocks from the house and BIL called again. The plane has loaded and backed away from the gate, but they are experiencing some sort of warning light in the cockpit, so they're going to sit there till they can have it checked by a mechanic.
The soonest it can arrive now is going to be around 1:00am, and that's only if they fix whatever the problem is on the aircraft quickly.
This is going to be a long night.