SQL & PL/SQL

Hi,
I have a requirement that i need to schedule a job using oracle scheduler daily at 7AM and 7 PM,presently i have
a code for scheduler which will run daily at 11O clock night which is working fine,i am adding that code,presently i am using 11G, Please help me.

BEGIN
DBMS_SCHEDULER.create_job

( job_name => 'employee_mv_job_dblink',
job_type => 'PLSQL_BLOCK',
job_action => 'begin employee_mv_refresh;commit;end;',
repeat_interval => 'FREQ=daily;dbyhour=23;byminute=0;bysecond=0 ',
enabled => TRUE,
comments => 'Test Auto Refresh'
);
END;

Thanks in Advance