Second/third century CE. See generally E.L.Bowie in OCD(3) s.v. Xenophon(2); FGrH 419.
[1] The transmitted text of the novel Ephesiaca is in fact in 5 books. Perhaps the Suda, or its source, Hesychius included a scribal error, or was simply mistaken. Alternatively, many scholars, following K. Buerger (Hermes 27 [1892] 36-67) and E. Rohde (Der griechische Roman und seine Vorlaufer 3 [Leipzig 1914] 429 n.1), believe that the received text is an epitome of a now lost original. But for a challenge to this view see J.N. O'Sullivan, Xenophon of Ephesus (Berlin 1995).