When i got my juvenile panther chameleon of 3 months of age the lowest he's been in was 65's and he was ok. However i dunno what species need such a low temperature drop maybe a more experienced member can help you there.
Montanes, like jacksons, are from high mountain, rainy areas that can get quite chilly, esp at night.
Even when I take them outside on a warm day, they will only stay in the sun a short while before looking for shade.
They also do not move as fast as panthers and veileds, so they dont have as much stored energy.