Heidegger's Bible Handbook: Nahum: Chronology

4.  An account of the time in which he prophesied is sought out.

The time of the prophecy of Nahum is not expressly set forth, and so it is left to be discerned from the Prophecy itself.  The Hebrews in Seder Olam, and Abarbanel also, refer it to the times of Manasseh, whom they say was deliberately not expressed, as unworthy on account of evil deeds.  Clement of Alexandria, book I, Stromata, refers it to the time of Jehoiakim, and makes him later than Ezekiel.  Others otherwise.  But if, as it appears, the ruin of Sennacherib is described by the Prophet in Nahum 1:13, it could be gathered, and that not implausibly, that he was a σύγχρονον/contemporary of Isaiah.