I have a high output t5 UVB and a 6500k grow light so it's still pretty light. Opening the window with the light off is at 81. Window closed and the basking spot went to 87-90. All during fall the basking temp stayed at 82-85
I did that in the summer with my Jackson - she just thought we were having a cloudy day - she should be fine with it shut off for a couple of hours mid day. What I did was to feed her early let her do a bit of basking before I turned it off-and turned it on a while before the lights went out for bed time.
You can move it back a little or use a lower watt bulb also - I think I changed light bulbs almost every week last fall- It would be 85 outside one day and 50 the next.