SQL> select current_time from dual;
select current_time from dual
ORA-00904: "CURRENT_TIME": invalid identifier

SQL> select sys.standard.current_time from dual;
select sys.standard.current_time from dual
ORA-06552: PL/SQL: Statement ignored
ORA-06553: PLS-302: component 'CURRENT_TIME' must be declared

  ...
  function current_date return date;
  function current_time return TIME_TZ_UNCONSTRAINED;
  function current_timestamp return TIMESTAMP_TZ_UNCONSTRAINED;