This had been gone for a few days for LAS-PHL-LAS, but a fare for February 25 popped up today. It is the redeye from LAS with a 12 hour layover, but I booked it. I guess I will take the train into the city and explore for a few hours. As an AA Platinum I get the Move Up for free, so if the 6pm flight isn't full I can get onto it without a charge.