It will be COLD to VERY COLD at night and maybe during the day also. Hiking in Zion now could be life threatening all of the hiking is pretty much UP and water and cold make for slick footing. But if you go DONT forget to think about one of the places that the wife and I have been and just fell in love with
Monument valley
We have always sought out the more obscure places to visit, Monument Valley is so vast and so,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,

MONUMENT VALLEY!!!! for a lack of better words. As Grizz said Grand Canyon is well worth the time so is Black Canyon of the Gunnison National Park, Mesa Verde Nat Park all in the general area that you are thinking about.