pl/pgsql and returns timestamp type

Hi all,

I cannot to get this to run... I think I am mistaking some basic concept or I have a big brain-lock . Somebody know what is the problem to execute this function ?

Thanks in advance...

--====================================
DROP TABLE test;
CREATE TABLE test
(
clave numeric(7,0) not null,
PRIMARY KEY (clave)
) WITHOUT OIDS;
--====================================
DROP FUNCTION f_test(numeric(7,0), numeric(7,0));
CREATE OR REPLACE FUNCTION f_test(numeric(7,0), numeric(7,0)) RETURNS timestamp AS '
DECLARE
p_datod ALIAS FOR $1;
p_datoh ALIAS FOR $2;
--
tdesde timestamp;
thasta timestamp;
BEGIN
tdesde := now();
--
FOR X IN p_datod..p_datoh LOOP
INSERT INTO test VALUES (x);
END LOOP;
--
thasta := now() - tdesde;
RETURN thasta;
COMMIT;
END;
' LANGUAGE 'plpgsql';
--====================================
select f_test(1,9);