Its a good idea to have a 10 to 15 degree drop in temps for night time sleeping. What kind of cham do you have? I know for veileds or panthers those temps are perfectly fine without having to use any nightime heating elements.
Yeah your cham should be fine at night with those temps. No need for any nightime bulbs or anything. Just be sure the cage has dried before lights out. I mist my cages about 2 hrs before I turn off the lights for the night. That gives the cage 2hrs to dry out fully. You just dont want to have a wet cage when they sleep. That can cause Upper Resp Infections.