I have some thoughts on this, but a question first. What does your schema look like? Clearly, you need to handle alot of this stuff a DB and using a database driven solution, I would think, would be required here.

I realize that is not a Perl answer but I am not sure your post is a Perl questions as much as it is an algorithm question. That is is fine, but I wanted to be clear on that.

My only other thought on it is to use Class::Date for handling the date calculation, storage, and calculation. I like the OO interface that it uses.

I did something like this recently, and would be happy to rehash that with you directly. Feel free to email me outside PM is you want to bounce some ideas around.