Version 11.3.1 first came out March 7, 2023 to early testers. As a peon, I didn't get 11.3.6 until April 8 2023 or 32 days after public announcement.
Verson 11.4.1 first came out May 11, 2023 to early testers. I got 11.4.2 on June 21, 2023 - 41 days.
Personally I don't recall announcements on "employee testing" historically (may have missed it) but my 11.3/11.4 experiences were when influencers started getting it. Now it looks like employee release of v12 with .1 around November 24, 2023 plus or minus. I'm with you on your guesstimate, perhaps a little sooner on #3 (assuming #1 and #2 are correct). I dare say the "public" version might be more like 12.3.5 though. Would love to be a fly on the wall foe that rollout discussion.
Bottom line - I doubt I'll see v12 of anything until 4 to 6 weeks after public influencers get their hands on it.