I think early October will be quieter than September as long as it’s outside of half term. People have caught on that September used to be dead and because of this, it no longer is. Plus most students don’t start until right at the end of the month, some even October. Couple this with a lack of international travel and I expect that September will be busy but pleasantly so, as I’m not summer holiday busy but busy enough for an atmosphere. I expect most coaster queues to be between 30-60 minutes, maybe more for The Smiler and Wickerman.
Also, with the staffing issues the park is facing, operations may be affected which results in longer queues regardless of guest numbers.
If you’re serious about avoiding queues, I would recommend getting to the park at 0915 (as I’m through the turnstiles) and heading straight to The Smiler. You’ll be one of the first ones on at 10am. Then go and do Thirteen and Rita (don’t bother with Roller Disco - you’ll have had better Waltzer rides at fun fairs). Then head to FV for Galactica and Nemesis then work your way back through Gloomy Wood, Katanga Canyon and Mutiny Bay. Have lunch, then ride Spinball, potentially buy a fast track for Oblivion, then do whatever else until the end of the day. Make Wickerman your last ride and join the queue at ride close time. It’ll have had all day to warm up and it’ll be running as fast as anything!