he can prolly take it colder overnight than you would be comfortable with.
maintaining his daytime temps is all you need to stress over.
some keepers here keep jacksons outdoors where it gets into
the 30's and 40's at night.
"Jackson's Chameleons, like other reptiles regulate their own body temperature and it is thus important to provide them with a temperature gradient inside their enclosure. The best ambient temperature during the day for Jackson's Chameleons is fairly cool, between 65 and 75 degrees Fahrenheit. By placing the basking bulb approximately 8-10 inches away from a basking perch inside the enclosure, a basking spot of approximately 80-85 degrees Fahrenheit is achieved. This arrangement provides the warmest temperatures directly under the heat bulb and cooler temps lower down in the enclosures. Additionally, chameleons do well with a night temperature drop so no additional heat source is needed at night as long as your temps stay above the mid to high 40s and the chameleons are able to bask in the morning."