As seen throughout Paul’s letters, the day of YHWH is associated with the judgment of the wicked, the resurrection of the dead, and the coming kingdom of the Messiah. Rather than redefining common Jewish apocalyptic expectations, it seems that Paul was primarily concerned  with pastoral needs and faithful discipleship in light of such expectations. 

The Jewish apocalyptic hope is the presumed goal in which all discipleship finds completion (cf. Rom. 2:5; 1 Cor. 1:8; 2 Cor. 1:14; Phil. 1:6; etc.). - John P. Harrigan