Yes, I changed the DTW-LAS to the earlier flight that will arrive at 9:03pm already. My problem is that the 4:10pm flight is too early not too late. There's no need to check for an earlier flight. Northwest has a codeshare flight from RIC-CLE and CLE-LAS (operated by CO) but they refused to put my relative on these flights. Probably I'll get a refund and buy a new ticket with CO.