Poor wrong 'scholar'.
In determining dating systems for the relevant period, one can choose from Nisan/accession, Nisan/non-accession, Tishri/accession or Tishri/non-accession dating.
When considering 2 Kings 25:1-8 (specifically, verses 1, 2 & 8), using Nisan/non-accession or Tishri/accession dating for kings of Judah cannot be reconciled with any of the dating systems for Nebuchadnezzar's reign.
It is evident from Ezekiel that the author uses Tishri-based dating for enumerating years of exile. However if Ezekiel 33:21 is considered in a vacuum and it is further assumed that most manuscripts and translations (including the NWT) are wrong and that Ezekiel 'really' learned of Jerusalem's fall in the 11th year of exile, this still cannot be reconciled with 2 Kings using Tishri/accession dating for kings of Judah or for using Nisan/accession or Tishri/accession dating for Babylon; further, unless it is assumed the author of Ezekiel counts years of exile from Nisan of 597, using Nisan/accession dating for Judah is also impossible.
Comparison of 2 Kings 24:12 with the Babylonian interpolation at Jeremiah 52:28 confirms that the author of 2 Kings uses Nisan/non-accession dating for Babylonian kings rather than Tishri/non-accession dating. The book of Jeremiah uses the same dating as in 2 Kings (e.g. compare 2 Kings 25:1 and Jeremiah 39:1), and Jeremiah 36:1 & 9 confirms that the author uses Tishri/non-accession dating for Judah rather than Nisan/accession dating (or the other systems already ruled out).
Hence the only possible placement of the siege on Jerusalem resulting in its destruction is from early 589 BCE until mid 587 BCE (the duration also being unaffected if the events are moved backwards 20 years according to the Watch Tower Society's errant Neo-Babylonain chronology), giving a length of approximately 30 months.