I have a Doggy Door, so my guys are used to running outside whenever they want. I don't think that cool/cold weather has much of an effect on the frequency, but possibly the lengths of their outings. During the warmer months, they frequently spend hours outside, lounging in the Sun, chasing Squirrels and playing. I have a lot of Glass/windows/Patio Door viewing that area, so it's not hard to keep an eye on them.
My guys are in very good shape. I have a 2 story house, and they "monitor" the property from the second floor windows, and frequently run out to the back of the property, to "defend" their territory
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