In Cat. xiv. 14, Cyril speaks in the Plural of the Emperors then reigning (οἱ νῦν βασιλεῖς) as having completed the building (ἐξειργάσαντο) and embellishment of the great Church of the Resurrection.  This can only apply to the sons of Constantine, Constans and Constantius, and as Constans died early in 350, the Lectures must have been delivered before that year.