Oracle 18c

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CREATE TABLE conv_process_run_time (
  START_TIME       TIMESTAMP(6),
  END_TIME         TIMESTAMP(6),
  PROCESS_RUN_TIME INTERVAL DAY(3) TO SECOND(6)
                   GENERATED ALWAYS AS (END_TIME - START_TIME)
);
INSERT INTO conv_process_run_time (START_TIME, END_TIME)
SELECT TIMESTAMP '2022-08-09 20:45:20.631429', TIMESTAMP '2022-08-09 20:45:23.257592' FROM DUAL UNION ALL
SELECT TIMESTAMP '2022-08-09 20:45:24.211717', TIMESTAMP '2022-08-09 20:45:24.896982' FROM DUAL UNION ALL
SELECT TIMESTAMP '2022-08-09 20:45:25.414725', TIMESTAMP '2022-08-09 20:45:27.375699' FROM DUAL UNION ALL
SELECT TIMESTAMP '2022-08-09 20:45:34.608107', TIMESTAMP '2022-08-09 20:45:35.027469' FROM DUAL UNION ALL
SELECT TIMESTAMP '2022-08-09 20:45:35.341021', TIMESTAMP '2022-08-09 20:45:42.104194' FROM DUAL UNION ALL
SELECT TIMESTAMP '2022-08-09 20:50:43.314294', TIMESTAMP '2022-08-09 20:53:05.335864' FROM DUAL;
6 rows affected

SELECT   NUMTODSINTERVAL (SUM (EXTRACT (DAY FROM PROCESS_RUN_TIME)), 'DAY')
       + NUMTODSINTERVAL (SUM (EXTRACT (HOUR FROM PROCESS_RUN_TIME)), 'HOUR')
       + NUMTODSINTERVAL (SUM (EXTRACT (MINUTE FROM PROCESS_RUN_TIME)),
                          'MINUTE')
       + NUMTODSINTERVAL (SUM (EXTRACT (SECOND FROM PROCESS_RUN_TIME)),
                          'SECOND')
          AS SUM_OF_TIME
  FROM CONV_PROCESS_RUN_TIME;


SUM_OF_TIME


+000000000 00:02:34.476507000


DROP TABLE conv_process_run_time;
CREATE TABLE conv_process_run_time (
  START_TIME       TIMESTAMP(6),
  END_TIME         TIMESTAMP(6),
  PROCESS_RUN_TIME VARCHAR2(50)
                   GENERATED ALWAYS AS (TO_CHAR(END_TIME - START_TIME))
);
INSERT INTO conv_process_run_time (START_TIME, END_TIME)
SELECT TIMESTAMP '2022-08-09 20:45:20.631429', TIMESTAMP '2022-08-09 20:45:23.257592' FROM DUAL UNION ALL
SELECT TIMESTAMP '2022-08-09 20:45:24.211717', TIMESTAMP '2022-08-09 20:45:24.896982' FROM DUAL UNION ALL
SELECT TIMESTAMP '2022-08-09 20:45:25.414725', TIMESTAMP '2022-08-09 20:45:27.375699' FROM DUAL UNION ALL
SELECT TIMESTAMP '2022-08-09 20:45:34.608107', TIMESTAMP '2022-08-09 20:45:35.027469' FROM DUAL UNION ALL
SELECT TIMESTAMP '2022-08-09 20:45:35.341021', TIMESTAMP '2022-08-09 20:45:42.104194' FROM DUAL UNION ALL
SELECT TIMESTAMP '2022-08-09 20:50:43.314294', TIMESTAMP '2022-08-09 20:53:05.335864' FROM DUAL;
6 rows affected

SELECT   NUMTODSINTERVAL (SUM (EXTRACT (DAY FROM PROCESS_RUN_TIME)), 'DAY')
       + NUMTODSINTERVAL (SUM (EXTRACT (HOUR FROM PROCESS_RUN_TIME)), 'HOUR')
       + NUMTODSINTERVAL (SUM (EXTRACT (MINUTE FROM PROCESS_RUN_TIME)),
                          'MINUTE')
       + NUMTODSINTERVAL (SUM (EXTRACT (SECOND FROM PROCESS_RUN_TIME)),
                          'SECOND')
          AS SUM_OF_TIME
  FROM CONV_PROCESS_RUN_TIME;
ORA-30076: invalid extract field for extract source

SELECT   NUMTODSINTERVAL (SUM (EXTRACT (DAY FROM END_TIME - START_TIME)), 'DAY')
       + NUMTODSINTERVAL (SUM (EXTRACT (HOUR FROM END_TIME - START_TIME)), 'HOUR')
       + NUMTODSINTERVAL (SUM (EXTRACT (MINUTE FROM END_TIME - START_TIME)),
                          'MINUTE')
       + NUMTODSINTERVAL (SUM (EXTRACT (SECOND FROM END_TIME - START_TIME)),
                          'SECOND')
          AS SUM_OF_TIME
  FROM CONV_PROCESS_RUN_TIME;


SUM_OF_TIME


+000000000 00:02:34.476507000