declare
job number;
begin
dbms_job.submit(job,
'procedure_name;',
trunc(sysdate)+23/48,
'trunc(sysdate)+1+23/48');
end;
the trunc(sysdate)+ 23/48 means today at 11:30am.
trunc(sysdate)+1+23/48 means tomorrow at 11:30am.
The command is submitted with the trunc(sysdate) command, so that the job will always start at 11:30. If submitted as 11:30 with an interval of 24 hours, it is possible for the begin time to move back, if the job takes a long time to run.