How to interpret timestamps stored as 10-digit negative integers? I've inherited an undocumented MS Access database where the date/time values are stored in an INT column and the majority of values I've seen so far are 10-digit negative integers. 

How do you process these as if they were DATETIME in SQL queries? 

If it simply can't be done through SQL and must instead be done through a programming/scripting language, what maths/process is required to transform these values into human-readable dates and times?

Example values:
-1358667448, -1358667348, -1358667248

The data was captured during the period 2006-2019 so the timestamps will be within that time frame.
Per Your comment the only place the values show as time stamps is in the application. You don't have access to the applications code.

The only possible solution, is to get a handful of actual time values shown in the application and relate them to values in the field, than figure how the difference is calculated. Then you will need to recalculate the values and add them to your database.  

I strongly suggest that you do not replace the source data.  Possibly add columns to the table with the correctly formatted dates.