Job oracle runs on its own

I have this job:

DBMS_JOB.SUBMIT(RT_job,'pkg_rt_semaforo.prc_rt_semaforo;',sysdate+0.00034722);
commit;

The sysdate + 30 segundos works fine, I am not parameterizing INTERVALO , but apparently the job is running again and again.

Should there then be an Interval by default?

Or what should you parameterize, so that it does not run again?