I came across the following 3 flights, which have to be in the running for worst three flights in the US--each for a different reason. All flights "redeyes" on Spirit.
SEA-BWI. Departs at 10:40pm, arrives at 6:48am. 5h8m in the air.
OAK-BWI. Departs at 4:45pm, arrives at 1:00am. 5h15m in the air.
SAN-BWI. Departs at 8:59pm, arrives at 5:00am. 5h1m in the air.
Each a similar length in the vaunted Spirit seat. The arrival times are what makes this so hard to gauge. Is 1am worse than 5am? Do you really want to arrive at the start of rush hour at 6:48am? But can that be worse for a human than either of the first 2 options?
I flew on Alaska Airlines from SEA-DFW departed at 11:50 PM arrived DFW at 5:20 AM in First Class bad times yes but I slept some during the flight and had a few drinks and the midnight snack provided.