Normally I would recommend that the menstrual cycle is charted to pin-point ovulation (you can also do this with a temperature chart). Usually intermittent dosing can start anywhere in the two weeks leading up to menstruaton. But I don't know enough about partial-hysterectomies, such as your case Season, where the ovaries are still intact, to say that this method would be 100% effective.
Intermittent dosing in this case might depend more on when you start experiencing mood symptoms in this time window, and for this you should also draw up a chart to pinpoint when it is in your cycle that you start feeling particularly bad emotionally, etc., then once you have an approximate time (day 18, 21 of your cycle etc.) you can safely assume that taking the meds a day or so before the expected time will be helpful.
Hope this helps to answer your question, maybe someone else here on the forum has some more helpful info. on this, help me out girls!
PS: The whole issue of the meds needing up to 2 weeks or more to build up in one's system is not applicable in the case of PMDD treatment, this is only necessary when treating severe clinical depressions, etc, where much higher concentrations of the active ingredient is required in the blood stream.