Time to change engine oil

Change the oil. The reason is that just setting the constant temperature changes around the car will cause some condensation to build up inside the engine. This can lead to rust and corrosion inside the engine. Also, the moisture will be absorbed by the additives in the oil and can make it corrosive as well. Normally this would all get boiled off when the engine got up to temperature while driving but you do not drive it enough to remove all that is building up.
For your driving habits I would suggest changing the oil at least every six months. Unless you start driving it more often. I would also try to drive it at least once a month and get it up to full operating temperature. That will ensure that oil gets splashed and sprayed around inside the engine to help protect it.