1,4 is primary key based on which sorting is done. This U will be knowing.
Now for that compare condition:
25,10 is the first date location. 55,10 is the second location.
CH is the format.
LT will check for the difference in dates, only those matching the condition will be selected.
You don't need to do a SORT to do this - you can just do a COPY. And LT (less than) is the correct comparison operator for the stated requirement, not LE (less than or equal to). The DFSORT job would be: