The term “the last” is not intended to direct our thoughts to a timeline as if these seven plagues describe what’s to happen in the (thin) slice of time just before Christ returns (in contrast to previous expressions of God’s wrath in the seals and the trumpets, as if they occur earlier). The term “last” catches the notion of ultimate, the fullest expression of God’s wrath. That is also why with them God’s wrath can be described as “finished.”
1 Then I saw another sign in heaven, great and amazing, seven angels with seven plagues, which are the last, for with them the wrath of God is finished.