Ditto minus the creating ficticous scenarios in my head. Let's see, where do I even start......
Yeah, my record is 6 hours and 1 minute. But that was because a friend told me that she had studied for six hours at a time before and I wanted to beat that. But I was listening to music the whole time I didn't absorb very much.
Typically my attention span starts to run low after about half an hour. This was a concern that bothered me for years. But over time I've developed lots of little tricks to work around the issue. Now, I can say that it's not a big problem in my life.
But your case sounds extreme enough that you might want to consider riddilin or something. Have you done that yet?
The last time I addressed this issue was here, where you can go if you want to learn more about my situation:
How can I be more introverted