Wow, your dad is an elder and he is surfing the net for anti-apostate websites!? He is disobeying the Society's firm advice that JW's should only do research using sources of information authorised by the Society.
Firstly, tell your father that you will only read that website if he reads Carl Olof Jonsson's book or Ray Franz's book. Why should he expect you to read non-authorised research supporting the Watchtower Society on this matter if he is not prepared to read alternative research opposing the Society's views? Otherwise he is a hypocrite.
Then point out to him that the whole 607v586 argument is moot anyway, because the symbolic 'tree' that was chopped down was never Jerusalem. If he likes surfing websites on these matters then refer him to this one http://www.bric.uk.com/Appendix.html#App18
THE VISION OF THE FELLED TREE.
This second and last dream vision God gave to Nebuchadnezzar was of an immense symbolic tree, visible to the extremity of the whole earth which had a figurative heart of a man, it had good foliage and enough fruit to feed everybody. At a time set, a 'holy watcher' gives the command to chop this tree down but to leave its stump in the earth for a period of 'seven times', during this seven times its symbolic heart of a man would change to that of a beast. After the 'seven times' runs out, God would set up a Kingdom over the Earth and he would present it to the lowliest one of mankind.
Daniel again explains its significance to Nebuchadnezzar. He tells him the tree represented the Babylonian king and world power. At an appointed time a 'holy angel' of God would make a proclamation to chop the tree down. God manipulated world events to see to it that this Babylonian world power was chopped down. The world powers following would not have a man's heart but would act as if they had a beast's heart until a period of time referred to as 'seven times' lapsed and then God would set up his Kingdom over the world of mankind (Daniel chapter 4).
Nebuchadnezzar again undergoes a small scale physical portrayal of this situation by going insane for 7 years acting like a beast (beasts heart given the tree).
TWO VISIONS OF BABYLONIAN DYNASTY
These two visions were specifically given by God to Nebuchadnezzar because they both started from him and related to the same subject. The head of gold in the first statue vision and the tree in his second vision were both confirmed as representing Nebuchadnezzar's Babylonian dynasty. The subject was the passing of time from the Babylonian world power until the take over of world rulership by God's Kingdom. Nebuchadnezzar experienced minor illustrative fulfilment's of both of these visions but they were obviously not the main application or meaning of the visions, he was a puppet used to act out greater events. This must be the case, because the vision was not completed with him, the Most high did not become the ruler of mankind when Nebuchadnezzar regained his sanity seven years later (Dan 4:22-37).
This vision dealt with the subject of subsequent world rulerships, ending when God's rulership takes over. The event from the cutting down of the tree spans a period of 'seven times'. So how long is this seven times? When does it start and when does it finish?
First; when does it start? We are told the tree represents Nebuchadnezzar, or more accurately the Babylonian dynasty. So when was it chopped down? According to the vision at a time when a proclamation is given by the 'watcher' or 'holy one'. When did this proclamation occur? The answer is in the very next chapter following the account of the tree vision inserted out of chapter time sequence. If the writer deliberately linked them together is he trying to tell us something?
THE DECREE OF THE HOLY WATCHER
The following chapter 5 of Daniel records what happened on the very last day of this Babylonian dynasty. Belshazzar the ruling descendant of Nebuchadnezzar, was holding a feast when a holy watcher arrives and marks out a decree, the hand of an angel materialises and writes four words on the wall, Mene, Mene, Tekel, Peres. The kings knees knock in terror at this event, understandable, he eventually summonses Daniel to explain the angel's written proclamation.
Daniel directly links this proclamation written on the wall, back to the tree vision that he had explained many years earlier to his forefather Nebuchadnezzar. He reminded Belshazzar that the most high God gave Nebuchadnezzar his kingdom, greatness, dignity and majesty but he became arrogant needing to be pulled down a peg or two by God (he went crazy for seven years) until he appreciated that it was God who gave him his position (Daniel 5:18-21) .
Likewise Belshazzar and his Babylonian dynasty were going to be pulled down because he also did not recognise that Yahweh had been using the Babylonians as his servant, backing their control of the Earth's nations by means of his power. This backing was about to run out, as the prescribed 70 year period had reached its end. Before Daniel explained the meaning of the words written on the wall by the holy watcher, he linked them back to the prophetic tree vision that Nebuchadnezzar had received some 50 odd years earlier (Daniel 4:23-37 with Daniel 5:18-21) .
Daniel now proceeds to read and interpret the words on the wall, telling Belshazzar that the number of days God allocated the Babylonian dynasty, had run out. The 70 year period (Jeremiah 25:12) had been measured off and the designated time for its end had arrived, his Babylonian kingdom was about to be given over to the Persians.
THE BABYLONIAN TREE CUT DOWN
God manoeuvred Cyrus the Persian to take over world rulership cutting down the Babylonian dynasty, (Isaiah 44:28, 45:1) . That very night, as foretold 77 years earlier by Jeremiah, the Persians captured Babylon and became the next world dynasty. Jeremiah said that when the Jewish exiles had served out their required seventy years punishment sentence under the Babylonian's then God would call an accounting against Babylon and would end their dynasty.
In the year 538 BC, the seventy years of exile ran out, Cyrus captured Babylon and Belshazzar was killed. God's ex-servant, the Babylonian dynasty was now cut down. In 538 BC the tree in Nebuchadnezzar dream, representing this Babylonian dynasty, received its proclamation from the 'holy watcher' to "Chop the tree down" by way of the angels writing on the wall. This command of the watcher to cut the Babylonian Dynasty down was immediately carried out by Cyrus wielding the conquerors sword, the Babylonian tree fell to as foretold.
The next world power had arrived on the scene, the Persians! From now on the descending chain of world powers would take a much more beast like aggressive attitude, the prophecy had said that the heart of man would be taken away and replaced by the heart of a beast (Daniel 4:16) just as the metals in the statue dream diminished in value.
SEVEN TIMES?
Establishing the date for the chopping down of the tree as 538 BC, we can set the starting date for the seven times. But how long is seven times, and when do they finish? Are they one and the same as the Gentile times referred to by Jesus at Luke 21:24 "Jerusalem will be trampled on by the nations (Gentiles) until the times of the nations (Gentiles) are completed (fulfilled)".
Seven in the scriptures is a number that signifies 'completeness', or 'bringing a period or work to a completion'. In historical sections of the scriptures, seven frequently occurs to denote 'completeness' or 'finishing a work completely' Jos 6: 2-4, 15, 1Ki 18:42-44, 2Ki 5:10, 12 Ps 12:6, Pr 24:16, Ps 119:164.
TIMES is translated in the scriptures ten times from the Aramaic word "iddan" as 'an appointed time period' or 'set season'.
The phrase Seven Times carries the scriptural meaning: 'an appointed time period set for completely finishing some activity'.
If the seven times start to count when the tree is chopped down in 538 BC, (when the gold of the head changed to the silver of the chest in the statue vision) then 'an appointed time period set for completely finishing the activity' would follow ending with the presenting of the Kingdom of God's rulership to the one whom God approves, scriptures identify this one as Jesus Christ.