The dispute over the year 607 BCE or 587/586 BCE is, in my opinion, unnecessary, if(!) this date would be decisive, to calculate (chronological speculation) 2520 years and determine the beginning of the reign of Jesus Christ.
The entire theological construction (more accurately: chronological speculation) concerning the "2520" years is flawed, or if you will, problematic. Every single point of this calculation is problematic, and the possible collapse at one single point of the entire calculation leads to the inevitable collapse of everything else, or the impossibility of continuing the calculation. With some irony one could say that you will never even get to the question of 607 BCE or 587/586 BCE, because the earlier calculation steps already fail and do not allow (non-violently and rationally!!!) to proceed further...
Single points:
1. Jesus made it clear in Acts 1:7 that neither χρονους (times) or καιρους (appointed times), nor the day or hour (Matt. 24:36) of His own coming can be known. If anyone attempts to overcome this, such as Russell, who claimed that in 1914 faithful Christians would be raptured to heaven and the reign of Christ would begin, this is a false prophecy. It does not change the fact that many others tried to do this long before Russell. As early as the 2nd century, for example, Hippolytus of Rome was converting 70 weeks to 490 years from the book of Daniel (system: a day per year) - he began a series of experiments with Bible numerals that successively alternated: from 666, through 1000, 1260. All of these early medieval attempts failed, so as time increased, it was necessary to duplicate these numerals or shift the starting date, etc., etc.
If you take seriously (you don't have to!) Jesus' own words about the impossibility of knowing the exact time of his coming and the sign of his coming, and not the attempts of various "Russells", then even the year 607 BCE or 586 BCE need not trouble you in this regard...
Let's move on.
2. JWs claim that the Aramaic term "idan" used in Dan 4:16 (25) (NWT) means year. The seven "idan" should be "seven years" when the government of Nebuchadnezzar was taken away. If the writer of the book of Daniel had wanted or should have used the Aramaic term for a year, then he would have written "schena" as in Dan 6:1 (62 years of life) or Dan 7:1 (the first year of the reign), likewise the Aramaic passages in the book of Ezra e.g. Ezra 4:24; 5:11 or 6:3 etc. But the Aramaic term for "year" in Dan 4:16 is not found. That alone, is enough to seriously doubt the "seven years" in Dan 4:16.
The mere occurrence of the word "idan" in the book of Daniel, does not make it possible, to determine exactly what chronological length the word "idan" expresses. The LXX Greek version usually translates the term as καιρος (see Acts 1:7 above), which would correspond to the meaning of "a certain period of time," with only the context determining the approximate duration.
Thus, for example, in Dan 2:8 (first occurrence), Nebuchadnezzar threatens his counselors that they want to get "idan" i.e. "time" (cf. the following verse 9 - and the synonym "seman") before he, the king, forgets his dream. In any case, it was so long before the king's work tasks would make it impossible to return to this riddle. It probably couldn't have been long, and even shorter than "idan", the king is annoyed. He decides in less time than "idan", namely, to kill all his advisors. Daniel then in Dan 2:16 begs for "time" i.e. "seman", a time roughly equivalent to "idan", to explain the dream. According to Dan 2:19, the "seman" lasted only one night. In one night God reveals the content of the dream and its interpretation.
Another example: Dan 3:5. Nebuchadnezzar builds a golden statue and commands that at the time of "idan" when everyone hears music playing, they must bow down to the statue. Then in Dan 3:7 it is stated that "at the time" when the music began to play, the writer used for the concept of time, a synonym for "idan" as in Dan 2:9 and in the form of the Aramaic "seman" i.e. time. At the appointed time of "idan" or "seman" the music plays. Does "idan"//"seman" refer only to the time when the music is playing? Probably yes, because the punishment for not fulfilling the extortionate listening to music was to come, according to Dan 3:6, "at that time"//"at that hour". And the denunciators, according to Dan 3:8, came to the king at "seman" (cf. LXX: καιρος) to complain against the Jews.
Also in the passages of Daniel chapter 4, we find a similar picture: Dan 4:16 (25) The NWT uses "idan" to establish the time limit of the seven "idans". Were they weeks, months, or the risings/setting of a star or constellation? In any case, it was not one "idan" to grow long hair and fingernails, but seven "idans", a time limit which according to Dan 4:34 (NWT) is made up more of "days" ("at the end of those days").
Conclusion: in terms of the meaning of the Aramaic "idan", it can be seen that it is a temporal concept that expresses an arbitrarily fixed length of time, usually in (hours) days (for night prayer or when music is playing and shortly thereafter), weeks (the king's work tasks) or months (hair and nail growth). Only the context determines how long the "idan" lasts.
From this perspective, if the "idan" in Dan 4:16 (25) NWT does not have to be a year long, and apparently it does not, then the consideration of counting the 2520 years further is completely unnecessary.
3. JWs (and some others in the present and past) claim that the 42 months and 1260 days in Rev 11:2-3 must be recalculated in the "day=year" formula. Nowhere is the necessity for any recalculation given this text of Rev 11:2-3 stated. And if this calculation worked in biblical times, it was at God's direct instruction. It is up to the one making this claim to prove that God told him to do so...
But to judge the accuracy of the "day=year" conversion in Rev 11:2-3, a simple thing will suffice: if JWs claim that 1260 days is 1260 years, then they have the following problem: In the passage regarding the two "witnesses" of Rev 11:3 and the duration of their prophesying i.e. 1260 days, it is further written (Rev 11:9 (11)) that their dead bodies will lie in the "great city" for "three and a half days". The JWs in their interpretation of Revelation claim that these "three and a half days" are "three and a half years", from 1916 to 1919, and of course refers only to selected persons among the JWs of the time.
But then, the two witnesses who preach 1260 days according to Rev 11:3 must also preach 1260 years!!! Or do they not? Or do they? Or how? 😊 The dead will be dead for 3.5 years because day=year and 1260 days is also actually 1260 years, but no, it's 1260 days, no, it's 1260 years. So how many? 😊 And if we take into account that the apocalyptic locusts that the JWs identify as their preachers are supposed to do damage for 5 months (Rev 9:5), then they are supposed to do damage for 150 years, right? Or is there no day=year conversion here? Not to mention that the Beast from the Sea is supposed to work for 42 months (Rev. 13:5), which, keeping the day=year conversion, again conflicts with the JWs' interpretation of who this beast is.
The whole "day=year" recalculation is completely confusing and betrays JWs exegetical arbitrariness.
4. Astrophysical problem. Let us concede, despite the above arguments, that the 2520 days=year calculation is correct. Then the astrophysical problem arises. The 2520 "years" is actually the claim that it is 2520 "rotations of the Earth", around the Sun. And we come to the problem of determining the year: what type of astronomical year should be used? A tropical year with a duration about 20 minutes shorter (365 days, 5 hours, 48 minutes, 45 seconds) than a sidereal year (365 days, 6 hours, 9 minutes, 9.45 seconds)? Without accounting for the variable length of each type of astronomical year, that 20 minutes over 2520 years makes a difference of about 35 days. Ironically, this confirms what Jesus said in Mat 24:36: no one knows about the hour and day.
And the main question: do we even know which type of year Jesus will follow when He comes? If we include another claim of the JWs, namely their calculation of the Passover, in addition to their reasoning about year types, or more accurately, calendarism, then the question becomes even more complicated. The JWs use a kind of luni-solar calendar, based on Jewish tradition, to prove that their calculation of Passover, and their calculation alone, is the accurate one. As a result, they celebrate the original, annual feast according to the solar calendar twice a year according to the lunisolar tradition... I'll leave the conversion of 2520 years back according to the lunisolar calendar to the Gregorian calendar to them.
Result: there's really no need to bother with 607 BCE. For those who argue that the chronological speculation with the 2520 year year is correct, there are so many obstacles and problems ahead, in my opinion, that proving 607 BCE may not even happen.