Charles Ellicott 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)

The month Tebeth. —This extended from the new moon in January to that in February; the name occurs only here. The fifth Egyptian month, lasting from December 20 to January 20, was called Tybi. The time referred to in the verse will be the January or February of the year 478 B.C., and must have been very shortly after Xerxes’ return to Susa from the West. The long delay in replacing Vashti is simply explained by the long absence of Xerxes in Greece.