Установка фиксированной sysdate : Oracle

ALTER SYSTEM SET fixed_date = '2007-01-27-11:50:00';

create or replace procedure datefix (fixit in varchar2 default 'none') 
is
begin
execute immediate 'ALTER SYSTEM SET fixed_date ='''|| fixit ||'''';
end;
/
grant execute on datefix to public;

exec sys.datefix('2013-07-28-11:50:00');
select to_char(sysdate,'DD-MM-YYYY HH24:MI:SS') from dual;