Albert Barnes Commentary Esther 2:16

"So Esther was taken unto king Ahasuerus into his house royal in the tenth month, which is the month Tebeth, in the seventh year of his reign." — Esther 2:16 (ASV)

Tebeth (compare the corresponding Egyptian month, “Tobi” or “Tubi”), corresponded nearly to our January.

In the seventh year of his reign - In December, 479 B.C., or January, 478 B.C. Xerxes left Sardis for Susa in, or soon after, September, 479 B.C. It has been regarded as a “difficulty” that Vashti’s place, declared vacant in 483 B.C., was not filled until the end of 479 B.C., four years afterward. But since two years out of the four had been occupied by the Grecian expedition, the objection cannot be considered very significant.