Neptunes/Timbaland/Eminem era: late 1998 - 2002

50 Cent/glam rap/crunk era: 2003 - mid 2005

snap/ringtone rap era: late 2005 - 2007

autotune/pop rap era: 2008 - mid 2009

Drake/alternative rap era: late 2009 - 2012

I did posts like this a while ago. I grouped the eras a bit more broadly than you, but I like your divisions as well.

1997–2006: Silver Age of Hip-Hop/Shiny Suit Era/Jiggy Era/Bling Era/Glam Rap Era/Pop Gangsta Era/Jersey Shirt and Headband Era/Silky R&B Crossover Era

Began in 1997 with Biggie's death and the rise of Ma$e, Puff Daddy, and Master P. Ended in 2005-06 when ringtone rap got popular, Eminem went on hiatus after Proof's death, J. Dilla died, and Nas released Hip-Hop Is Dead.

2006–2014: Bronze Age of Hip-Hop/Ringtone Snap Era/Yolo Swag Era/Melodic Electronic Melancholic Era/Pop Rap Era/AutoTune Era/Alternative Rap Era/Blog Era

Began in 2006–07 when Nas released Hip-Hop Is Dead, Soulja Boy released Crank That, and Kanye West's Graduation defeated 50 Cent's Curtis in a sales battle. Ended in 2014 when songs like No Type by Rae Sremmurd, Lifestyle by Rich Gang, and Trap Queen by Fetty Wap brought mumble rap and trap to a massive level of popularity.

I did posts like this a while ago. I grouped the eras a bit more broadly than you, but I like your divisions as well.

1997–2006: Silver Age of Hip-Hop/Shiny Suit Era/Jiggy Era/Bling Era/Glam Rap Era/Pop Gangsta Era/Jersey Shirt and Headband Era/Silky R&B Crossover Era

Began in 1997 with Biggie's death and the rise of Ma$e, Puff Daddy, and Master P. Ended in 2005-06 when ringtone rap got popular, Eminem went on hiatus after Proof's death, J. Dilla died, and Nas released Hip-Hop Is Dead.

2006–2014: Bronze Age of Hip-Hop/Ringtone Snap Era/Yolo Swag Era/Melodic Electronic Melancholic Era/Pop Rap Era/AutoTune Era/Alternative Rap Era/Blog Era

Began in 2006–07 when Nas released Hip-Hop Is Dead, Soulja Boy released Crank That, and Kanye West's Graduation defeated 50 Cent's Curtis in a sales battle. Ended in 2014 when songs like No Type by Rae Sremmurd, Lifestyle by Rich Gang, and Trap Queen by Fetty Wap brought mumble rap and trap to a massive level of popularity.

Thanks, yeah I was going for the most specific time divisions because a ringtone rap song from 2007 sounds much different than a song by Future or Migos from 2013 lol, but the broad divisions also make sense if it's not about sound changes.