It's possible to simulate permanent night? How? By those sliders (Sunrise Begin, Sunrise End, Sunset Begin, Sunset End) or is it something more tricky?
On Climates on the right of the window you can see Weathers. Go to World>Weathers there you can create one, you can make a fake always night type by putting the same value on all the day cycles, you can even add only stars on the sky.
Done that go back on your climate and on the Weathers tab add your weather.
Then in the World Space on Climate put your custom one.
Now this is just a trick, it doesn't make the permanent night real in terms of time, you can still wait or sleep and have time passing. You can disable waiting on the World Spaces window. there is a checkbox with written "Can't Wait", just check this.