My DD cluster-fed in the evenings too, from only a few days of age. She wasn't sleeping quite that long immediately, but at least 5-6 hrs from around 11pm or midnight as well. Don't tell anyone!

As long as she is having plenty of wet and dirty nappies, thriving and it sounds like she is having plenty of bfs at other times, as the others have said, nothing to worry about. You might just be lucky (enjoy it, babies have a habit of not sticking to any particular pattern for too long!).