Oracle 18c

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create table source_of_data (user_date date, user_hours varchar(100))
insert into source_of_data values(to_date('20220323', 'yyyymmdd'),  '12:01:02')
1 rows affected

select to_timestamp(to_char(user_date, 'yyyymmdd') || ' ' || user_hours ,'YYYYMMDD HH:MI:SS') as_timestamp
from source_of_data;

AS_TIMESTAMP

23-MAR-22 12.01.02.000000000