Your answers as follows:
1. The Bible does not provide for the 'moment' the 70 years ended but does provide historical and chronological for its ending: 2 Chron.36:20-23; Ezra 1:1, 3:1. The 'first year of Cyrus and the 'seventh month are described for the end of the period with the Decree of Cyrus and the Return of the Exiles. However, we can express the matter in terms of the Gregorian Calendar as September 29, 537 BCE for the beginning of Tishri, the seventh month or in terms of the Julian Calendar would be October 5. I can consult the tables and get down to the very time of day in hours and minutes based on the Vernal Equinox and Lunations of the Moon for 537 BCE if you so require.
2. The Bible or ancient history does not provide guarantees but simply sufficient facts and historical data which enables the historian and Chronologist to determine and secure 537 BCE as the date for the Return.
3. Celebrated WT scholars along with my good self declare 539 CE as a Pivotal Date for dating the OT and is universally supported by scholarship as the correct date for the Fall of Babylon.
I agree with Thiele that the Bible does not present dates in a BCE format.
If the Jews had followed Jeremiah's warning and repented then they would not have lost their Temple, City and Land for their judgement was provisional but as we know the rest is history.
The two months after the destruction of Jerusalem in 607 BCE in the fifth month indeed provide adequate time for the Jews to flee and leave the Land totally desolate by the beginning of the seventh month, 607 BCE. With Jehovah nothing is impossible for he is the Great Timekeeper.