That sort of drop in temps at night is definitely not going to work long term. Wide temperature swings can put them off their food...as well as the low temps put them at risk of developing respiratory infections if continuously exposed.

There are a few different options you could consider and try...

1. Get a small space heater to keep the room warmer at night (or at least that area of the room if it's a big room)

2. Get a red heat lamp for over the cage (the red colored light won't bother them at night) and switch it on at night.

3. Insulate at least three walls of the glass tank with foam-board. (This will help with security issues as well, as some ball pythons don't care for the open exposed feeling that glass walls provide)

4. Wrap the tank in a blanket at night.

The blanket and/or insulation may or may not work and you may have to tweak different ideas to come up with an optimal solution for your particular circumstances.