I can't see why it would be against the rules to advertise an event that won't be held for several months... but the question is, is your target audience even on campus right now and will your time and effort be wasted? Definitely check with the campus Panhellenic.
But common sense suggests that you aren't holding any events during the silence period, and you should be allowed to generally promote your organization to the campus-at-large 365 days a year.
Oh and as a follow up to my original post, our PNM happily pledged her first choice (ZTA) at Baylor and is loving her sorority and university!
