You get no credit whatsoever. Even people who are fully board certified in say the UK and are teaching faculty here are not and wont ever be members of the ABMS (American Board of Medical Specialties) unless they do a full residency. Previous to a few years ago, you could get path credit for year in another ACGMEcert residency/internship but this is no longer the case. In addition, there is no research credit that is offered anymore.
3 years to AP or CP cert and 4 years if you want to get a combined AP/CP cert (which now is a like a unique cert that counts as only 1 towards your lifetime cap of 3 AMBS certs).