CCC 1001 When? Definitively “at the last day,” “at the end of the world.”1 Indeed, the resurrection of the dead is closely associated with Christ’s Parousia:
For the Lord himself will descend from heaven, with a cry of command, with the archangel’s call, and with the sound of the trumpet of God. And the dead in Christ will rise first.2

1 Jn 6: 39-40,44,54; 11:24; LG 48 § 3.
2 1 Thess 4:16.