Well there is a way. Go to background tab, then you see a day and night cycle. You gotta drag the sun down and it will be night. you can do before its night, that the night is a bit farther away then the whole top. Then you animation has a time that you can set. Sadly you cant use multiple times, because the time doesnt cycle automatic at all.
Oh sorry, i didnt knew you question was like that. Sorry!