Heidegger's Bible Handbook: 2 Corinthians: Time of Writing
6. The time of the writing of the Epistle, namely, the year following the writing of the former Epistle, is elicited.
Saint Paul appears to have written this Epistle neither immediately after the first, nor much after. For, when from Ephesus, where he wrote the first Epistle, he loosed, traveling through Macedonia, in Macedonia he was found by Titus, whom he had sent ahead to Corinth, so that he might ascertain their repentance, and in what manner the first Epistle was received, 2 Corinthians 7:5. And, when he had received the contributions from the Macedonians, he again sends Titus from Macedonia to Corinth, 2 Corinthians 8:6, 15, 16, and with him that brother, whose praise was in the Gospel throughout all the Churches, that is, Luke, 2 Corinthians 8:18, 19, unto this end, that they might take care that the contributions of the Corinthians be ready against the coming of Paul, 2 Corinthians 9:3-5. And this Epistle appears to have been sent through the agency of these two, having been written while Saint Paul was traveling through Macedonia, and so in the following year, after the first was written. But, whether it was written at Philippi, as the subscription relates, or from another city of Macedonia, Nicopolis, for example, as Baronius insists, it cannot be determined with certainty; although, that it was not written at Nicopolis, is demonstrated with probable argument by Louis Cappel in the Appendix to his Historiæ Apostolicæ, page 72, against Baronius.
 1 Corinthians 16:5.