When to add blueberry flavoring

Hey all. I have a friend who has a blueberry porter he has been chasing for many many years. Long story short, he has managed to track down a recipe, but it is not very explicit on all of the details. I can work most of it out, but I am unsure when to add the blueberry puree. Seems like some people like to add after the boil, but before the wort is chilled all the way, some to the primary fermenter. Is this one of those things that doesn't matter that much? Cause if not, I think I would prefer to add to the wort before it is chilled all the way for sanitary reasons. I have never brewed with any kind of fruit additions, so this is a new one for me.

Let me hear your thoughts!