I am by no means an expert on the subject seeing as I only started easy with my son a little over 8 weeks ago, when he was 7 weeks old, but I fed him when he woke up "early". At that age the rooting reflex should still be present so if you're unsure whether she's hungry or not, you could always check that. In my opinion, again this is what I have been doing, the next 3h block should start after you've fed her rather than after the time at which she was supposed to be fed.