Macbeth invokes the night because he has engaged murderers to kill Banquo and Fleance. So he feels that when nightfall comes he will be free of the threat of Banquo and his heirs.
He has come to appreciate the night and the evil that can be wrought and how quickly, in the dark, a problem is solved, for Macbeth of course. The night, which has an association with the forces of darkness, which Macbeth has now become intimately linked, for now will satisfy his fear of threats to his crown. When night comes, and Banquo and Fleance are killed, never to pose a threat or raise a suspicion, Macbeth believes that he will be free to enjoy being king.
In the darkness, Macbeth takes care of his problems, when he thinks that no one can see, but he is deluding himself.