Oracle 18c

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create table table1 (col1 varchar2(32),    start_date_time timestamp(9),                  end_date_time timestamp(9));
insert into table1
select 'Test1',  to_timestamp('01-06-19 11:43:35.927422000', 'DD-MM-YY HH24:MI:SS.FF'),  to_timestamp('01-06-19 11:44:20.127907000', 'DD-MM-YY HH24:MI:SS.FF') from dual union all
select 'Test2',  to_timestamp('01-06-19 11:44:28.703518000', 'DD-MM-YY HH24:MI:SS.FF'),  to_timestamp('01-06-19 11:45:06.538883000', 'DD-MM-YY HH24:MI:SS.FF') from dual union all
select 'Test3',  to_timestamp('01-06-19 11:42:18.784477000', 'DD-MM-YY HH24:MI:SS.FF'),  to_timestamp('01-06-19 11:42:27.635102000', 'DD-MM-YY HH24:MI:SS.FF') from dual
/
3 rows affected

select numtodsinterval(  
  sum(  
    (sysdate+(end_date_time - start_date_time) - sysdate) * 24 * 60 * 60
  )  
  , 'second'  
)  
from table1;  


NUMTODSINTERVAL(SUM((SYSDATE+(END_DATE_TIME-START_DATE_TIME)-SYSDATE)*24*60*60),'SECOND')


+000000000 00:01:29.000000000


select numtodsinterval(  
  sum(  
    (sysdate+(end_date_time - start_date_time) - sysdate) * 24 * 60 * 60
    + extract(second from (end_date_time - start_date_time)) - trunc(extract(second from (end_date_time - start_date_time))) 
  )  
  , 'second'  
)  
from table1;  


NUMTODSINTERVAL(SUM((SYSDATE+(END_DATE_TIME-START_DATE_TIME)-SYSDATE)*24*60*60+EXTRACT(SECONDFROM(END_DATE_TIME-START_DATE_TIME))-TRUNC(EXTRACT(SECONDFROM(END_DATE_TIME-START_DATE_TIME)))),'SECOND')


+000000000 00:01:30.886475000