I'm not getting you correctly.. But if u want to add 5minutes to an date say for example:
select sysdate,sysdate +interval '5' minute from dual
What error are your getting? Without knowing the error - all we can do is guess at the cause/fix.
You have to use TO_CHAR because NAME_IN and COPY use varchar2 as datatype. There is a application-property BUILTIN_DATE_FORMAT (don't remember the exact name) where you get the format you need to use, it should look similar to
vcDateFormat:=GET_APPLICATION_PROPERTY(BUILTIN_DATE_FORMAT); copy(TO_CHAR(TO_DATE(name_in('date.start_datetime'), vcDateFormat) +5/24/60 , vcDateFormat), 'DATE.END_DATETIME');