I believe the room only cancellation policy requires cancellation a minimum of 5 days before check in to avoid penalty. You can book a package anytime.
All people on package have to be on the dining plan though.
I believe you need to add a dining plan 2 or 3 days before your trip? For some reason I think I always say 3 days and the truth is 2? Once you add dining you change your room only to a package and full payment would be due if it was within the 30 day window.