how to find the exact time taken by a query?

[julian]

Run as SYS prvtutil.plb script. You will find it in $ORACLE_HOME/rdbms/admin/

Then, still as SYS:

SVRMGR> GRANT EXECUTE ON DBMS_SYSTEM TO USER_NAME;

Then, as USER_NAME, create a synonym:

SVRMGR> CREATE SYNONYM DBMS_SYSTEM FOR SYS.DBMS_SYSTEM;