Run a Job (DBMS_Scheduler) at 11:30 am and 5:30 pm every day

Question

Version:10gR2
I want to run a job at at 11:30 am and 5:30 pm every day. After setting
start_date        =>  sysdate,
repeat_interval   =>  'freq = daily;Don't know how to set BYHOUR and BYMINUTE parameters twice in a day

Answer 1

You'll probably want a repeat interval like this:
FREQ=DAILY;BYHOUR=11,17;BYMINUTE=30;BYSECOND=0The DBMS_SCHEDULER package provides a procedure called EVALUATE_CALENDAR_STRING which allows you to test different repeat intervals and see if they meet your requirements. They even provide example code that you can easily copy and modify.
The documentation also goes into great detail about the Calendaring Syntax. It's worth a read.
For example here is the code I used to test your requirement.
DECLARE
        start_date        TIMESTAMP;
        return_date_after TIMESTAMP;
        next_run_date     TIMESTAMP;
BEGIN
        start_date := systimestamp;
        return_date_after := start_date;
        FOR i IN 1..5 LOOP
                DBMS_SCHEDULER.EVALUATE_CALENDAR_STRING
                ( 'FREQ=DAILY;BYHOUR=11,17;BYMINUTE=30;BYSECOND=0'
                , start_date
                , return_date_after
                , next_run_date
                DBMS_OUTPUT.PUT_LINE('next_run_date: ' || next_run_date);
                return_date_after := next_run_date;
        END LOOP;
END;
/