I think because it differs for most children & each tooth!! Matilda's first tooth broke through twice before it stayed out of the gums and then it took another week before it was obviously a tooth, her second tooth just showed up over night & its already almost as long as her first tooth...within 2 weeks. She is cutting both top teeth at the moment & one of them broke through Monday but isn't there today

So I'm sorry I have no answers only that they are all different 8-[