Charles Ellicott Commentary Zechariah 7:1

"And it came to pass in the fourth year of king Darius, that the word of Jehovah came unto Zechariah in the fourth [day] of the ninth month, even in Chislev." — Zechariah 7:1 (ASV)

Fourth year ... This was in 518 B.C., the second year after the commencement of the rebuilding of the Temple, and about two years before its completion.