Temperature questions

Hello, just had a couple questions about my baby bci. I have a basking spot around 90 degrees on one side of tub. The other side is around 80 on the surface and 77 a couple inches above. Uth on the hot side and the cool side I'm heating my whole bedroom. Yuck. But my question is, I have read that the cool side can get as low as 75 degrees. Would this be ok if I let the cool side drop this low? I have an oil heater plugged into a programmable thermostat and I can set it to drop during the night and go back up in the morning. Is this a good idea?
Wish I had a separate snake room, but unfortunately I dont so he is in my bedroom.

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My BI's cool side has probably dropped to as low as 68 during the coldest winter nights, but when I turn the heater on in the critter room it's more like an ambient temp of 72-76 at night. As long as they have access to a warm spot they can handle slightly cooler ambient temps.