Oracle 18c

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CREATE TABLE schedule_hdr (schedule_id, schedule_name) AS
SELECT 1, 'Schedule 1' FROM DUAL UNION ALL
SELECT 2, 'Schedule 2' FROM DUAL;
2 rows affected

ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS'
WITH random_times ( schedule_id, schedule_name, datetime, lvl ) AS (
  SELECT schedule_id,
         schedule_name, 
         TRUNC(sysdate)
         + NUMTODSINTERVAL( FLOOR(DBMS_RANDOM.VALUE(0,19*60)), 'MINUTE' ),
         1
  FROM   schedule_hdr
UNION ALL
  SELECT schedule_id,
         schedule_name, 
         datetime + NUMTODSINTERVAL(FLOOR(DBMS_RANDOM.VALUE(6,11)), 'MINUTE'),
         lvl + 1
  FROM   random_times
  WHERE  lvl < 5
)
SELECT schedule_id,
       schedule_name,
       datetime
FROM   random_times
ORDER BY schedule_id, datetime;


SCHEDULE_ID
SCHEDULE_NAME
DATETIME


1
Schedule 1
2020-07-11 05:13:00

1
Schedule 1
2020-07-11 05:23:00

1
Schedule 1
2020-07-11 05:32:00

1
Schedule 1
2020-07-11 05:38:00

1
Schedule 1
2020-07-11 05:45:00

2
Schedule 2
2020-07-11 10:56:00

2
Schedule 2
2020-07-11 11:02:00

2
Schedule 2
2020-07-11 11:09:00

2
Schedule 2
2020-07-11 11:19:00

2
Schedule 2
2020-07-11 11:29:00

SCHEDULE_ID	SCHEDULE_NAME	DATETIME
1	Schedule 1	2020-07-11 05:13:00
1	Schedule 1	2020-07-11 05:23:00
1	Schedule 1	2020-07-11 05:32:00
1	Schedule 1	2020-07-11 05:38:00
1	Schedule 1	2020-07-11 05:45:00
2	Schedule 2	2020-07-11 10:56:00
2	Schedule 2	2020-07-11 11:02:00
2	Schedule 2	2020-07-11 11:09:00
2	Schedule 2	2020-07-11 11:19:00
2	Schedule 2	2020-07-11 11:29:00