I'm not sure if I fully understand your question, but, I will attempt to answer. Most US MBA programs start in the fall. You apply the year prior and there are various applications deadlines. You may only apply to a school once per cycle (per year) but you can apply in any of the deadlines (usually one is in the fall, one in winter and one in early spring). There different deadlines are referred to as "Rounds". The convetional wisdom is that it is a little bit easier to get in when you apply to an early round. But, applicants are accepted from all of the rounds (most schools have 3, some may have 2 and a few have 4).
Once you apply in a cycle (for instance, right now applicants are applying for a fall 2011 start time) you must wait to see if you are admitted/waitlisted/denied. If you are not accepted, you can apply the following year. You do not apply to the same school more than once for the same start class. If you aren't accepted in the fall, the thought is that your candidacy won't improve drastically in another 2 months for the winter or spring application deadline. If there is something that drastically changes your candidacy (a huge promotion or a much improved GMAT score) you can notify the admissions office and let them know. They may take it into account (and they will absolutely take this into account if you are waitlisted).
If you already anticipate being a much better candidate later in the application cycle (in the "winter" round) then I would hold off and apply then (if you are expecting a promotion or plan to retake your GMAT, etc.).
Many candidates will apply to some schools in the first round and another school or two in the second round. This usually helps with time management and enables you to put in the strongest essays/application possible.
Please let me know if you need further clarifcation. But, you apply to a school once each year!
