now() in loop statement

Hello,

What is wrong with this function because the mytime variable contain the
same value in each iteration:
CREATE OR REPLACE FUNCTION public.time_test()
RETURNS int4 AS
'
DECLARE
count int4;
mytime timestamp;
BEGIN
count := 0;
mytime := now();
while count <= 25 loop
mytime := now();
RAISE NOTICE \'Time: %\',mytime;
count := count + 1;
end loop;
RAISE NOTICE \'Count: %\',count;
RETURN count;
END;
'
LANGUAGE 'plpgsql' VOLATILE;

the result is:
NOTICE: Time: 2003-09-29 15:52:06.745317
.
.
.
NOTICE: Time: 2003-09-29 15:52:06.745317 --same with the first value!!!
NOTICE: Count: 26

Thanks.