Actually, the poster made no error. Those are the times listed in the Northwest system (can been seen on nwa.com) as well as in various CRS...

And by the way, don't assume it's just an innocent mistake.

CRS displays flights in order of flight time. So if one was to search for MKE-LAS, NW's flight would come first, followed by YX.

Given the predatory nature of these flights, I wouldn't find it too surprising if this was intentional to put the NW flight at the top listing.