Original: In his description of Tartarus, Hesiod says further that Hemera (day), who is Nyx's daughter, left Tartarus just as Nyx entered it; when Hemera returned, Nyx left.
Simplified: In his description of Tartarus, Hesiod says further that Hemera "day", who is now Night's sister rather than daughter, left Tartarus just as Nyx entered it; when Hemera returned, Nyx left.