How soon/late have you heard "I love you?"?

I'm in a happy relationship of about three months, one that might even go the distance some day. I have not, however, heard the L word yet, although I feel it for my part. This shouldn't concern me, but the couple of other times I've heard it, it has been within probably three weeks of beginning the relationship. Is there, in your opinion, some threshold at play with saying I Love You? (i.e., some edict of "If you haven't heard it within X number of months/years, you never will")? Is three months unreasonably soon? Unjustly late? Just wanting some opinions/experiences.