How to Concat Datetime without Losing Second Precision
You are losing seconds because the default format for converting datetime to string is the same as:

SELECT CONVERT(char(19), GETDATE(), 0);


Which outputs (for me, right now):

Oct 30 2018  2:02PM


You can try something more like this:

SELECT CONCAT
       (
         'ABC ', 
         CONVERT(char(19), GETDATE(), 25)
       );


Which outputs (again, for me, right now):

ABC 2018-10-30 14:02:55


If second aren't enough, just change char(19) to char(23). If that's still not enough, you can consider changing that column to datetime2 to get more precision.