In my opinion, mid 1996 to early 1998 was like a weird transitional period for the WWE, where there is real definitive moment that ended the New Gen era and started the Attitude Era. There are still some key moments that can be seen as the start of the Attitude Era:
>Austin wins the King of the Ring tournament and cuts his 3:16 promo [King of the Ring PPV, June 23rd 1996
>Hogan turns heel and the formation of the New World Order [Bash at the Beach PPV, July 7th 1996]
>The infamous "Pillman's Got A Gun" segment [RAW, November 4th 1996]
>Bret Hart snaps [RAW, March 17th 1997]
>The Austin-Hart Double-Turn [WrestleMania 13, March 23rd 1997]
>Shawn turns heel after accidentally screwing Taker [Summerslam, August 3rd 1997]
>The Montreal Screwjob [Survivor Series, November 9th 1997]
>The Austin vs Tyson segment [RAW IS WAR, January 19th 1998]
>Austin beats Michaels for the World Title and the Austin era has begun [WrestleMania, March 29th 1998]
I don't know what the answer may be, but these are the defining moments of the formation of the Attitude Era.
