Please do share your suggestions. Hyperfocus isn't the problem for people suffering ADHD. It's applying hyperfocus selectively on worthwhile tasks. "Neurotypicals'" best advice is usually "you just have to will it".
How I implemented this was to find a job that required me to take a train into work. This train was light commuter rail, only about 25 minutes. I brought a laptop with me and would sit with it balanced on my lap in a shaking (sometimes quite loud) train. At first it was very difficult to get into focus, but over a year I just found it easier and easier.
I think if I was to do it again, I'd probably find some dumb reason to leave the house every day. Perhaps I'd never keep breakfast food in the house and have to go walk or drive to the store every day for that day's breakfast, then sit in the parking lot or store cafe for thirty minutes. Perhaps I'd make a daily Starbucks routine, ensuring I'm there thirty minutes early every day. Or I'd convince myself to get to work early to beat the traffic, but then sit in the parking lot for 30 minutes.
It doesn't much matter how, all that matters is outcome.
What you're describing sounds a lot like the concept of "Deep Work" as popularized by Cal Newport. Unfortunately this is exactly where people with ADHD fail (or maybe it's just me).
I've been trying to set up a work routine, like the one you describe, for years now. Without much success so far. It doesn't even matter how high the stakes are or how close the deadline looms, I simply can't "force" myself to focus. It feels like every day the dices are rolled anew.
For over 20 years now, I've also been (on and off) trying to practice meditation and mindfulness even before this got popular and I still can't go 2 minutes without my thoughts wandering to what I want to do next.
But I nevertheless respect your effort and the results you achieved. There's a current thread about the application of Psylocybin to depression. Perhaps that one is interesting to you as well:
I am currently willing to try anything (except drugs) to help my attention. Pomodoro and meditation have helped me enormously in the past. But now, with kids at home, everything has taken a beating.
I'm very proud in some ways, so training my mind is satisfying to me on several levels. I love knowing that short of a knock on the head, no one can take this away from me, that I've forged this thing myself. It's only mine, can't be faked or bought, only earned through hard work. That's appealing to me. Likewise, I train my body, with heavy lifting, grueling rucking, challenging gymnastics, and fast running. I love that I can change parts of this form I inhabit to be my own, both inside and out. Sure I still have to wear my glasses and get sick etc, but I get a tremendous joy improving those things I can.
But in those that do, it's like a superpower. I spent several years training my hyperfocus to the point where, barring externalities like lack of sleep or food, I can engage it at will.
For challenging or creative tasks, it's like a superpower. I can go at levels far past most people's ability to focus. My entire mind will be engaged and thriving at full blast. Presentations, writing, designing, and creating I can do as easily as breathing.
There are real downsides, but I wouldn't trade them for anything.