I've read that four months is the minimum. While the extract isn't getting darker, subtle flavors are still extracting from the pods.
If you want to get really technical, the literature review put together by Garth at Heilala Vanilla (see the links page) has some firm technical data on the matter. I seem to recall that 6 months, aged on the beans, was ideal. I don't have the materials handy, though.
Four months should be fine, besides, who will really be able to tell the difference?
Your gift package sounds fantastic. I'm planning to do something similar, but I hadn't thought of giving vanilla beans as well.