I believe light has a far greater effect than temperature. The length of daylight hours, plus the color and intensity of the light as the sun gets lower. There is a dramatic reduction in UV in the light as the sun gets lower and UVA is an important circannual rhythm trigger.
In watching my aquatic turtles in a "semi-natural" pond for several decades, once we pass Oct 1st here, they simply aren't interested in food any more. It doesn't matter if we are having a warm or cold Sept/Oct - its always the same. Temperature will definitely effect how deeply they brumate and how much they have semi active periods. But the light "tells" them it is time to slow down and stop feeding.
Thank you. I was thinking the length of light had an important impact. I have read recommendations that say if you are not brumating your tortoise (I have a greek), you should provide 12-14 hours of light (including artificial?) per day. But if they go ahead and head for sleep in their dark hide at 4pm, what does an extra hour or two of artificial light provide? They don't actually receive it because they are tucked away. Also, what kind of artificial light is best for that 12-14 hours if you are choosing not to hibernate your tort? UVB?