Some rather snotty answers here. I used the library several years ago for some specific book, although I've now forgotten what it was. I found it excellent, and the staff were extremely helpful. I can't remember what the opening times were, and they don't seem to be on the Horniman website. I would drop in next time you're at the Horniman and see what they say. My recollection is that it was all anthropology, so if that's of interest you'll love it.