I-- was mourning three full weeks - The weeks are most probably dated from the time of the termination of the last vision. Calmet proves this by several reasons.

I Daniel.

Ezra 9:4,5 Then were assembled to me every one that trembled at the words of the God of Israel...

Nehemiah 1:4 And it came to pass, when I heard these words, that I sat down and wept, and mourned certain days, and fasted...

Psalm 42:9 I will say to God my rock, Why have you forgotten me? why go I mourning because of the oppression of the enemy?

Psalm 43:2 For you are the God of my strength: why do you cast me off? why go I mourning because of the oppression of the enemy?

Psalm 137:1-5 By the rivers of Babylon, there we sat down, yes, we wept, when we remembered Zion...

Isaiah 66:10 Rejoice you with Jerusalem, and be glad with her, all you that love her: rejoice for joy with her, all you that mourn for her:

Jeremiah 9:1 Oh that my head were waters, and my eyes a fountain of tears...

Matthew 9:15 And Jesus said to them, Can the children of the bridal chamber mourn, as long as the bridegroom is with them? but the days will come...

Romans 9:2 That I have great heaviness and continual sorrow in my heart.

James 4:9 Be afflicted, and mourn, and weep: let your laughter be turned to mourning, and your joy to heaviness.

Revelation 11:5 And if any man will hurt them, fire proceeds out of their mouth, and devours their enemies: and if any man will hurt them...

full weeks. Heb. weeks of days.

Daniel 9:24-27 Seventy weeks are determined on your people and on your holy city, to finish the transgression, and to make an end of sins...

Youthful Confessors
'But Daniel purposed in his heart that he would not defile himself with the portion of the king's meat, nor with the wine which he drank; therefore he requested of the prince of the eunuchs that he might not defile himself. 9. Now God had brought Daniel into favour and tender love with the prince of the eunuchs. 10. And the prince of the eunuchs said unto Daniel, I fear my lord the king, who hath appointed your meat and your drink; for why should he see your faces worse liking than the children which …
Alexander Maclaren—Expositions of Holy Scripture

Annunciation to Zacharias of the Birth of John the Baptist.
(at Jerusalem. Probably b.c. 6.) ^C Luke I. 5-25. ^c 5 There was in the days of Herod, the king of Judæa [a Jewish proselyte, an Idumæan or Edomite by birth, founder of the Herodian family, king of Judæa from b.c. 40 to a.d. 4, made such by the Roman Senate on the recommendation of Mark Antony and Octavius Cæsar], a certain priest named Zacharias, of the course [David divided the priests into twenty-four bodies or courses, each course serving in rotation one week in the temple …
J. W. McGarvey—The Four-Fold Gospel

Of a Private Fast.
That we may rightly perform a private fast, four things are to be observed:--First, The author; Secondly, The time and occasion; Thirdly, The manner; Fourthly, The ends of private fasting. 1. Of the Author. The first that ordained fasting was God himself in paradise; and it was the first law that God made, in commanding Adam to abstain from eating the forbidden fruit. God would not pronounce nor write his law without fasting (Lev. xxiii), and in his law commands all his people to fast. So does our …
Lewis Bayly—The Practice of Piety