Not a lot of people apply for N-600 so it is likely you won't get an answer, that processing time means it will take six months or less. N-600 is not a very transparent process, there is no tracking number or anything, unless they have changed this recently.
If you are doing it for a child you might or not be called for an interview (a mere formality, not like a N-400 interview). In my child's case they didn't invite us to an interview, they just issued the certificate.