1 hour 8 mins by salad bakersNaxxramas was speedrun on private servers in ~1 hr 30 minutes. My bet it will be done by APES in 1 hr 10 minutes on first/second run. Sub-1 hour in clean subsequent ones. Given its Classic and given the minority will achieve that, there's no sense whatsoever in running anything below Naxxramas as it is.
Get rid of your rose-colored glasses and enjoy the game for what it is supposed to be - fun and player interaction. There are other competetive games out there that make that aspect way more joyful and meaningful.