When using a texture for the sky, the amount of ambient light produced is relative to how bright the sky texture is, whether 'Add sunlight' is ticked or not.
'Add sunlight' just adds a very large distant sphere light to simulate the sun while using a sky texture.
There is a way ambient light could be switched off between certain hours, by setting the samples to 0 but this would require reading (the following values and) one of Emmanuel's special algorithms,
possibly using an 'if' statement?sunCalendar.get(Calendar.HOUR_OF_DAY)
sunCalendar.get(Calendar.MONTH) + 1
Doing so would only switch off the ambient light, the sky brightness would stay the same, seeing as in real life there is almost always some ambient light, this could produce an unnatural looking render.
Other ideas, I think built-in image manipulation would be too time consuming, plus there are lot of open source programs able to do this easily.
So to sum up:
Darker sky textures will always produce less ambient light (no matter what time is entered) so the best advice for anyone is, choose or make a sky texture, that represents the desired look you hope to achieve in the final render.
Hope this helps!
db4tech
