Bro is right, I've read the same. There's a big conspiracy debate over whether or not Japan sent the declaration in time, and/or if the US intentionally delayed allowing the declaration to be made in a timely manner so that they could declare Japan's attack as an unwarranted sneak attack, or whatever. It's something interesting to read about, if nothing else.

Regardless of what happened, however, I think it is agreed upon that the attack occurred before Japan's declaration of war was completed, for whatever reason, and thus that is how it is classified: an attack before a declaration. Regardless of Japan's intentions, the result could well be seen as the consequence of trying to declare a war and launch an attack so close together.

I might be mistaken, but I thought I read that they planned the attack first, and the declaration was decided second, as a sort of damage control for the decision of the attack. I think there was also dispute between Japanese leaders over whether or not the attack should have been made. Time to read up on it again, I suppose.