hh:mi offset from sysdate

test.sql

create table t (
  c date
);

insert into t (c) values (to_date('01.10.2019 06:45', 'mm-dd-yyyy hh24:mi'));
insert into t (c) values (to_date('01.10.2021 21:45', 'mm-dd-yyyy hh24:mi'));

select sysdate current_date,
   to_date(to_char(sysdate, 'dd-mm-yyyy') || to_char(c, 'hh24') || to_char(c, 'mi'), 'dd-mm-yyyyhh24mi') new_date,
   cast(to_date(to_char(sysdate, 'dd-mm-yyyy') || to_char(c, 'hh24') || to_char(c, 'mi'), 'dd-mm-yyyyhh24mi') as timestamp) - systimestamp diff,
   extract(hour from cast(to_date(to_char(sysdate, 'dd-mm-yyyy') || to_char(c, 'hh24') || to_char(c, 'mi'), 'dd-mm-yyyyhh24mi') as timestamp) - systimestamp) hour_diff,
   extract(minute from cast(to_date(to_char(sysdate, 'dd-mm-yyyy') || to_char(c, 'hh24') || to_char(c, 'mi'), 'dd-mm-yyyyhh24mi') as timestamp) - systimestamp) mi_diff,
   extract(hour from cast(to_date(to_char(sysdate, 'dd-mm-yyyy') || to_char(c, 'hh24') || to_char(c, 'mi'), 'dd-mm-yyyyhh24mi') as timestamp) - systimestamp) || ':' || abs(extract(minute from cast(to_date(to_char(sysdate, 'dd-mm-yyyy') || to_char(c, 'hh24') || to_char(c, 'mi'), 'dd-mm-yyyyhh24mi') as timestamp) - systimestamp)) res 
from t