I need something like this, but haven't been able to find anything. I'm mildly ASD and having time boxed todo items in an easy "this is what you need to do next, tick it off when it's done" way is basically the only thing that works for my brain. Many years ago I used to have a macOS menubar app that let you arrange your tasks on a timeline of the day, it was magnificent.
Thank you for sharing your experience.
I kept OwnTime strictly separate from todos. There are so many great apps for that. I would consider linking priorities into external todo apps, e.g. if it would be possible to deep link into a certain group of todos in the app of your choice. So you could go OwnTime -> priority -> switch to todos associated with that priority.