Matthew 2:7

Then Herod privily called the wise men

(τοτε Hηρωιδης λαθρα καλεσας τους μαγους). He had manifestly not told members of the Sanhedrin why he was concerned about the Messiah. So he conceals his motives to the Magi. And yet he "learned of them carefully" (εκριβωσεν), "learned exactly" or "accurately." He was anxious to see if the Jewish prophecy of the birthplace of the Messiah agreed with the indications of the star to the Magi. He kept to himself his purpose. The time of the appearing star (τον χρονον του φαινομενου αστερος) is not "the time when the star appeared," but the age of the star's appearance.