Effective today, September 22 2016, it will be the shortest time between the official reveal of a new Nintendo gaming platform, and its release date, barring any delays. I'm including all handhelds in this as well, although I'm not counting hardware revisions like the GBA SP, Game Boy Micro, DS Lite, and New 3DS XL. This includes Japanese versions of the same platform, so while the NES/Super NES may have had a shorter time between announcement and launch, they were based on an existing gaming platform that had already been released in Japan. Also, reveal does not equal announcement, so while the NX has been known about and announced by Nintendo for some time now, nothing about it bar its release date has been officially announced by Nintendo. I think this may also be the shortest time between the console reveal and release of any platform ever (not just Nintendo) but since there have been so many game consoles throughout history it's very difficult to make such a statement.



Game Boy Advance: Revealed on August 24, 2000 at Spaceworld. Launched March 21, 2001 = 6 months, 28 days.



Nintendo DS: Revealed on May 11, 2004 at Nintendo's E3 2004 conference. Launched November 21, 2004 = 6 months, 10 days.



Nintendo NX: Revealed (at absolute earliest) on September 22, 2016. Launched (at absolute latest) on March 31, 2017 = 6 months, 9 days.



EDIT: My apologies for putting "Officially" in the topic title. It should read "Currently". A delay, as many are pointing out, is very likely. I have put in a request to change it.