PL/SQL :: Return Past Timestamp Values On Base Of Input Hour To User Function

resolve issue while modified the user function code for returns the values as timestamps

---function code

create or replace
function fun_test_timestamp(P_HOUR varchar2) return varchar2
is
sql_stmt varchar2(1000);
begin

[Code].....

Input:-
select fun_test_timestamp('5') from dual;

Output:-

SELECT CURRENT_TIMESTAMP - INTERVAL '5' HOUR FROM DUAL;

Modified Fun Code:

create or replace
function fun_test_timestamp(P_HOUR varchar2) return timestamp
is
sql_stmt varchar2(1000);

[Code]...

Input:-
select fun_test_timestamp('5') from dual;

Output:-

ORA-00911: invalid character
ORA-06512: at "NETVERTEXTRUNK.FUN_TEST_TIMESTAMP", line 8
00911. 00000 - "invalid character"

*Cause:    identifiers may not start with any ASCII character other than letters and numbers. $#_ are also allowed after the first character. Identifiers enclosed by doublequotes may contain
any character other than a doublequote. Alternative quotes (q'#...#') cannot use spaces, tabs, or carriage returns as delimiters. For all other contexts, consult the SQL Language Reference Manual.

*Action: