My question involves a traffic ticket from the state of: California

I received a moving violation in July 2012 that I plan on disputing. I have an date to appear in February 2013, probably a date with a judge in May of 2013 to dispute it
If the judge grants me traffic school (or if I just pay the darn thing) in May of 2013, does that mean I can not go to traffic school for 18 months after May 2013 again, or 18 months after the original ticket date in July of 2012?

Is traffic school once every 18 months from the ticket, or once every 18 months from the completion of the traffic school date?

I have no other points/violations of any sort on my record if that makes any difference.

Thanks