I honestly have no idea. I actually doubt there's any specific thing that should happen or amount of time that should pass first, you just have to play it by ear. Of course, if you say it within like 3 days it may scare the other person away.. I think people are easily weirded out by people saying "I love you" too soon, I guess because a lot of people are desperate. Also, you should probably only say it when you feel like the other person is ready to say it too, because otherwise it makes things awkward if they can't respond with an "I love you too." But I wish "I love you" didn't have to be so political. I wish you could just say it when you feel it.