Temps can be anywhere from freezing to 80 degrees F. I ride to DV about a dozen times a year. It's EASILY a day trip. If you hustle, you can make it there within two hours from Vegas. Be sure to gas up in Pahrump, or you'll be paying much higher than normal.
Ride Badwater Road, starting from Shoshone. Eat lunch in Furnace Creek, then ride up to Dante's View. After that, you should still have at least a few hours of day light left. (This is riding conservatively and checking out the sights)