If a monthly schedule is defined with the 1st, 2nd, 3d, 4th, Last <Weekday> of N Month with a duration starting at a day that is after when the schedule would trigger for that month, the schedule still triggers (before the configured starting at day).
Example:
Third Saturday of June, 2012 is the 16th, configure the schedule to start at June 30, 2012. The schedule still triggers on June 16.
A simple work-around is to have the schedule start on any day of the first month when you want the schedule to trigger.