Just FYI they're doing road work at the Chisos Basin and the only road up or down is closed from 8-11 and 2-5. At least it was last week when we where there. And the times you can go up was packed due to Spring Break. May be easier now.
Must see's are Santa Elena(short hike with great scenery), window view (not really a hike at all but awesome and quick) and lost mine trail. (Good hike and awesome views.).
So so much to do but if you only have one day this is what I would do.
From top to bottom. My oldest illegally crossing into Mexico in Santa Elena, Boquillas Canyon, Earnst Tinaja trail.