YoYo, I'll answer your 2nd two questions first: Daniel's prophecy in chapter 4 is said to have been fulfilled upon Nebuchadnezzar. It's history, over and done with. No one knows for sure what the "appointed times of the nations" means. From Luke 21 it's pretty apparent that, whatever it means" the "times" began when Jerusalem was destroyed in 70 C.E. There is no clear Biblical indication when they were to end.
As for your comments about 2 Chronicles 36:21, it is apparent that you have no problem with the fact that your interpretation contradicts the absolutely clear statement in verse 20, which I have explained at length. If the Bible does not contradict itself, then how do you explain verse 20? Once you deal with this problem, we can move on in our discussion. Satisfying answers exist that do not result in contradictions.
As for Daniel 9:2, your claim that "Daniel also understood the 70 year prophesy that way" is without merit. The verse is quite ambiguous about just what Daniel meant when he said that he "discerned by the books the number of the years concerning which the word of Jehovah had occurred to Jeremiah the prophet, for fulfilling the devastations [chorbah, plural] of Jerusalem, [namely,] seventy years." The Society claims that Daniel saw ahead of time that the 70 years were about to end, but neither the verse nor the context supports that. Indeed, the context lends strong support to the idea that Daniel had already observed conditions that allowed him to conclude that the 70 years had already ended, as we will see below.
We need to get one point out of the way first, though. The word "devastations" (chorbah in Hebrew) is in the plural, so it certainly is not referring to just one period of devastation, namely, the time when the Jews were away from Jerusalem. Indeed, Jerusalem was "desolated" in the Hebrew sense a number of times. Daniel may well have had in mind the successive desolations and depopulations beginning in Nebuchadnezzar's accession year in 605 B.C. and ending with the complete destruction of Jerusalem in 587/6 B.C. This seems to have been how the translators of The Jerusalem Bible understood the passage, as they render Dan. 9:2 as follows:
"In the first years of his reign I, Daniel, was perusing the scriptures, counting over the number of years -- as revealed by Yahweh to the prophet Jeremiah -- that were to pass before the successive devastations of Jerusalem would come to an end, namely seventy years."
Of course, this is not a literal translation of Daniel's words, but one interpretation of his thought. There is not enough information in the Bible to be certain about exactly what Daniel had in mind.
Next we will consider the fact that the Hebrew word chorbah does not necessarily mean "completely desolated, without an inhabitant". It can mean just what the English word "devastated" means, namely, severely broken. Indeed, Jeremiah 25:18 states that Jerusalem and the cities of Judah would become "a devastated place, an object of astonishment, something to whistle at and a malediction, just as at this day." This prophecy was uttered "in the fourth year of Jehoiakim,... that is, the first year of Nebuchadnezzar" (Jer. 25:1). The phrase "just as at this day" seems to indicate that the devastation, to a certain degree, had already begun at this time, eighteen years prior to the destruction of Jerusalem.
That the word chorbah does not necessarily mean a state of desolation "without an inhabitant" can be seen from other texts which use the word. For example,
Ezekiel 33:24, 27 mentions "the inhabitants of these devastated places." Nehemiah wrote his book during a time when Jerusalem was inhabited, yet at Nehemiah
2:17 the city is said to be "devastated."
Now let's carefully compare what God tells the Jewish exiles in Babylon will happen at the end of the 70 years with what Daniel says actually did happen. Jeremiah 29:10-14 reads:
"10 For thus says the LORD, "When seventy years have been completed for Babylon, I will visit you and fulfill My good word to you, to bring you back to this place. 11 For I know the plans that I have for you," declares the LORD, "plans for welfare and not for calamity to give you a future and a hope. 12 Then you will call upon Me and come and pray to Me, and I will listen to you. 13 You will seek Me and find Me when you search for Me with all your heart. 14 I will be found by you," declares the LORD, "and I will restore your fortunes and will gather you from all the nations and from all the places where I have driven you," declares the LORD, "and I will bring you back to the place from where I sent you into exile."
Note carefully that God said that after the completion of 70 years "for Babylon", he would visit the Jews and return them from exile. This makes perfect sense. On the other hand, the Society's interpretation along with the NWT's rendering "seventy years at Babylon cannot both be correct, because if the captivity ended when the Jews arrived back in Judah, then they would still have been captive while they were still in Babylon, which contradicts the NWT's rendering that God would visit the Jews after "seventy years have been completed at Babylon".
Given the rather clear portrayal in Jeremiah 29 of what was going to occur, note how it matches up with what Daniel said did occur. Let's consider the first few verses of Daniel 9:
"In the first year of Darius ... who was made king over the kingdom of the Chaldeans"
Obviously, Daniel is describing a time immediately after the fall of Babylon. Having understood what Jeremiah wrote, including the above from 29:10-14, he knew that when he saw that Babylon had fallen, the 70 years of servitude must also have ended. Indeed, he goes on to write:
"in the first year of his reign, I, Daniel, observed in the books the number of the years which was revealed as the word of the LORD to Jeremiah the prophet for the completion of the desolations of Jerusalem, namely, seventy years."
Having concluded that the 70 years must have ended, Daniel proceeded to do exactly as God had said the Jews would do in Jer. 29:12-13. Dan. 9:3 reads:
"So I gave my attention to the Lord God to seek Him by prayer and supplications, with fasting, sackcloth and ashes."
After many more words of supplication, Daniel's prayers were answered, just as had been predicted in Jeremiah 29:14. Dan. 9:20-21 reads:
"Now while I was speaking and praying, and confessing my sin and the sin of my people Israel, and presenting my supplication before the LORD my God in behalf of the holy mountain of my God, while I was still speaking in prayer, then the man Gabriel, whom I had seen in the vision previously, came to me..."
So we find complete agreement in this interpretation between Jeremiah 29:10-14 and Daniel 9:1-23. On the other hand, the Watchtower interpretation contradicts what the Bible says and is self-contradictory. I think it's easy to understand that the Society's view on this is simply wrong.