When did Nebuzardan come to Jerusalem—on the seventh day of the month (per 2 Kings 25:8) or the tenth day (per Jeremiah 52:12)?

Given that Kings likely used Jeremiah as a source (or vice versa), the close similarity indicates a direct literary dependence, meaning one number is likely a copyist error. In ancient Hebrew script, the words for "seventh" and "tenth" look reasonably similar. "Seventh" is written as shin-beth-ayin-he while "tenth" is ayin-sin-yodh-resh. Beth and ayin look reasonably similar in ancient script, and since the text was originally unpointed, sin and shin would be indistinguishable. The difference between the first two letters of "seventh" and "tenth" is easily explainable as a common copyist error—visual confusion of similar letters and transposition.

When did Nebuzardan come to Jerusalem -- on the seventh or tenth (per Jeremiah 52:12) day of the month? There is no clear answer, but given that Kings likely used Jeremiah as a source, because of the close similarity indicating a direct (perhaps literary) dependence, 10 is more likely. 'Seventh' in Hebrew script looks reasonably similar to 'tenth', and the difference seems reasonably explainable as two common errors: confusion of similar letters because of their visual resemblance and transposition of letters. Both of these copyist errors are common in any manuscript transmission.