I have been having lots of problems with importing date fields.
This process illustrates my difficulty.

I have a ‘testdates’ CSV file:
ID Date in text Date as excel shortdate UNIX
1 11th November 1968 11/11/1968 -35942400
2 25th December 2002 25/12/2002 1040774400
3 29th January 2002 29/01/2002 1012262400
4 2nd August 2017 02/08/2017 1501632000
5 3rd October 1974 03/10/1974 149990400

I make a custom post type called ‘testdates’

I make a new field group for this post type:

I add a test entry.

I do an import of my CSV file using WPAllimport.

I make a view for these records:

 

The unixdate field works fine on the front end view….. but in the Admin view the unix column fails:

Sorted one way:

Sorted the other way: