Daniel 10:1

This vision is dated in the third year of Cyrus, that is, of his reign after the conquest of Babylon, his third year since Daniel became acquainted with him and a subject to him. Here is, I. A general idea of this prophecy (Dan 10:1): The thing was true; every word of God is so; it was true that Daniel had such a vision, and that such and such things were said. This he solemnly attests upon the word of a prophet. Et hoc paratus est verificare - He was prepared to verify it; and, if it was a word spoken from heaven, no doubt it is stedfast and may be depended upon. But the time appointed was long, as long as to the end of the reign of Antiochus, which was 300 years, a long time indeed when it is looked upon as to come. Nay, and because it is usual with the prophets to glance at things spiritual and eternal, there is that in this prophecy which looks in type as far forward as to the end of the world and the resurrection of the dead; and then he might well say, The time appointed was long. It was, however, made as plain to him as if it had been a history rather than a prophecy; he understood the thing; so distinctly was it delivered to him, and received by him, that he could say he had understanding of the vision.

— Matthew Henry's Concise Commentary (public domain)