Oracle 18c

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alter session set nls_timestamp_format = 'yyyy-mm-dd hh24:mi:ss';
alter session set nls_date_format = 'yyyy-mm-dd hh24:mi:ss';
with t as (
    select timestamp '2020-10-01 22:15:00' time_of_Day , 3 hours_to_add from dual
    union all select timestamp '2020-11-01 15:04:00', 4 from dual
)
select 
    t.*,
    time_of_day + hours_to_add/24 as_date, 
    time_of_day + hours_to_add * interval '1' hour as_timestamp
from t


TIME_OF_DAY
HOURS_TO_ADD
AS_DATE
AS_TIMESTAMP


2020-10-01 22:15:00
3
2020-10-02 01:15:00
2020-10-02 01:15:00

2020-11-01 15:04:00
4
2020-11-01 19:04:00
2020-11-01 19:04:00

TIME_OF_DAY	HOURS_TO_ADD	AS_DATE	AS_TIMESTAMP
2020-10-01 22:15:00	3	2020-10-02 01:15:00	2020-10-02 01:15:00
2020-11-01 15:04:00	4	2020-11-01 19:04:00	2020-11-01 19:04:00