Yes, but optimum for who?
Airliners have different zonal heating systems. This means that the whole cabin is often divided into two, three or four separate zones for automatic heating purposes. Given that any one zone may contain over a hundred passengers, it is impossible to find a temperature that will satisy or be optimum for everybody.
Where individual overhead blower vents are installed, the passenger has some small control over their own environment to the extent that they can cool themselves in a warm cabin, but these are by no means universal and even where fitted they don't suit everyone.
Automatic heating controls don't differentiate between night and day, they simply regulate to a set temperature at the location of the thermostats, much as the heating in your home does. People who are tired, or at the low point of their circadium rythmn will usually feel colder even though the ambient air temperature hasn't changed. On a night flight this often results in an increase in the number of people seeking an increase in temperature. Of course not everybody is affected by this and some will also find the increase uncomfortable.
Often (but not always) the temperature is controlled from the flight deck, and there can be few pilots who aren't just as frustrated at constant requests for temperature adjustments, often in reversal to a request made just a few minutes earlier that wouldn't have had time to take effect.
So to answer your question, the airlines usually do maintain an optimum temperature on board. It is normally around 24c. It is requests from passengers and crewmembers that results in alterations to this. With hundreds of individual comfort criteria to consider, and only two or three automatic thermostat zones, you begin to see the difficulty. Nevertheless we still try, and await advances in technology.