I don't speak SQL, but file_time_iso looks to be a 'widestring' field. I suspect that this is a regular text string that cannot be used directly in calculations or numeric comparisons.
It follows the ISO8601 format: yyyy-mm-ddTHH:MM:SS.SSS (where the capital T separates the date from the time).
You'd probably have to use a type conversion in your query, so that the file_time_iso can be compared to a date of your choice, but I really have no idea what command and syntax you'd have to use.. Sorry!