How does one select a 24 hour / type of time from DUAL?

Iím working on an app where the users are required to work / enter times in a 24 hour format.

Code:
-- this works 
SELECT to_date('16-JUL-2003 12:30:00','DD-MON-YYYY HH:MI:SS') FROM DUAL
-- this one creates an error Hour must be between 1 and 12 
SELECT to_date('16-JUL-2003 13:30:00','DD-MON-YYYY HH:MI:SS') FROM DUAL