scholar:
You said that "at" in the verse "When 70 years at Babylon are fulfilled" has a locative meaning in the sense of place or location and is similar to 'in Babylon'. So 70 years in Babylon.
You said that the land was vacated by the seventh month in 607 BCE .
And we have a round trip between Juda and Babylon of at least 6 months.
So seventh month of 607 BCE + 70 years in Babylon + 6 months round trip, in which year and month did they return when you add this up? Definitely not the month of Tishri in 537 BCE.