Names and references: STEPBible, Tyndale House Cambridge · CC BY 4.0 · coordinates: OpenBible.info Bible Geocoding · CC BY 4.0
How we know the date
ISBE identifies the Ahasuerus of Esther with Xerxes and gives his reign as a span rather than dating the book's events; Easton's puts the feast of Esther 1 in 479 BC. ISBE's article “Xerxes” (1915) gives a range, 485 BC to 465 BC; Easton's (1897), under “Esther” gives 479 BC. ISBE (1915), whose reckoning this stretch of the timeline follows, does not date it, so no single year is shown and the event is placed by its order in the narrative, between the years quoted.
Written in-house from the sources below · every year is a quotation
The sources, word for word
“Xerxes was king of Persia in 485-465 BC.”
“This took place about fifty-two years after the Return, the year of the great battles of Plataea and Mycale (B.C. 479).”