Following @Gruber hypothetical September schedule: Tuesday 15 September: Event. Friday 18 September: Preorders start. Monday-Tuesday 21-22. September: Reviews drop — Apple Watch on one day, iPad Air on the other. Thursday 24 September: New OSes released via Software Update. Friday 25 September: Products ship to customers and stores.
My guess is that we will get beta 8 this week followed by GM next week. Even if there is another beta after that (beta 9), this would be the shortest beta cycle for any major iOS release. https://daringfireball.net/2020/09/apple_time_flies_event