To convert character strings into numbers use the INPUT() function with an informat that understands how to convert the strings you have into dates. So if DUE_DATE has values like '01JAN2020' then use the DATE9. informat.
input(due_date,date9.)
If DUE_DATE has values like '01JAN2020 00:05:00' then you might be able to use the same statement as it will ignore all but the first 9 characters. But if some of the strings have less that 8 or 9 characters to represent the date, such as '01JAN20 00:05' then you might want to first remove the characters after the space.
input(scan(due_date,1,' '),date9.)
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