In case anyone is interested, Thorn has created find: [the material called sky], which changes colour and switches its material brightness depending on the hour of the day.
Currently, it should include the light material from 6:00am till 7:00pm COW Mean Time. of course, the true daylight of adelaide varies.
So if you have an outdoor location and you want it to brighten and darken depending on the time of day, put _dark_ in its material and create an object with _sky_ in its material.
Changes to the sky only occur during arrivals. In other words, you can't sit still and watch the sunset (and those who do are too rare to warrant yet another ticklock on the system).