The phrase "at that time" means the same thing as and intensifies the phrase "in those days." Alternate translation: "in those very days" or "at that very time" (See: [[rc://en/ta/man/jit/figs-doublet]])
The abstract noun "captivity" can be translated as a verbal clause, and it may be understood as a metaphor for Yahweh making the people prosper in a general sense. Alternate translation: "when I cause Judah and Jerusalem to live well again" or "free Judah and Jerusalem from those who had captured them" (See: [[rc://en/ta/man/jit/figs-abstractnouns]] and [[rc://en/ta/man/jit/figs-metaphor]])
The names of the cities are metaphors for the people who lived in the cities. Alternate translation: "the people of Judah and Jerusalem" (See: [[rc://en/ta/man/jit/figs-metaphor]])