While Daniel prayed in Daniel 9, a messenger reached him in swift flight at about the time of what?

Answer: The evening sacrifice

While Daniel was still praying, Gabriel came to him in swift flight about the time of the evening sacrifice (KJV: evening oblation).

“While I was speaking, praying, confessing my sin and that of my people Israel, and presenting my petition before the LORD my God concerning His holy mountain— while I was still praying, Gabriel, the man I had seen in the earlier vision, came to me in swift flight about the time of the evening sacrifice.”— Daniel 9:20-21 (BSB)