Oracle 21c

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CREATE TYPE date_range_obj AS OBJECT(
  start_date DATE,
  end_date   DATE
)
/
CREATE TABLE autoplanallocation (
  project_id  NUMBER,
  task_id     NUMBER,
  pref_start  DATE,
  pref_finish DATE
);
INSERT INTO autoplanallocation (project_id, task_id, pref_start, pref_finish)
VALUES (1, 2, DATE '1970-01-01', TRUNC(SYSDATE, 'MM'));
1 rows affected

INSERT INTO autoplanallocation (project_id, task_id, pref_start, pref_finish)
VALUES (1, 2, TRUNC(SYSDATE, 'YY'), SYSDATE);
1 rows affected

CREATE FUNCTION HCLT_GET_TASK_DATES(
  i_ownerid IN autoplanallocation.project_id%TYPE,
  i_itemid  IN autoplanallocation.task_id%TYPE
)
RETURN date_range_obj
IS
  v_range date_range_obj;
begin
  SELECT date_range_obj(MIN(pref_start), MAX(pref_finish))
  INTO   v_range
  FROM   autoplanallocation
  WHERE  project_id = i_ownerid
  AND    task_id = i_itemid;

  RETURN v_range;
END;
/
ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS'
SELECT HCLT_GET_TASK_DATES(1,2).start_date,
       HCLT_GET_TASK_DATES(1,2).end_date
FROM   DUAL;


HCLT_GET_TASK_DATES(1,2).START_DATE
HCLT_GET_TASK_DATES(1,2).END_DATE


1970-01-01 00:00:00
2022-03-31 20:29:25