Interesting take on it, I certainly resonate with the "Michigan weather making work the only thing to do" anecdote. I struggle with productivity, and feeling productive. and when I look back on times when I felt productive the attention thing does stand out. It occurred to me when I thought of myself as a younger programmer that I used to love the time between midnight and 3AM, there was literally nothing on TV to di…
It really works, and in a couple of days you'll likely have your focus back.
I started doing this "how long can I concentrate for" game in grad school in the 80s, and tried it again a few years ago when I was struggling. My concentration span started at a super-embarrassing couple of minutes at a time. In a couple of days I was back in the hour range, and before long it was as long as I needed. These days I, like you, seldom have tremendously long blocks like 4 hours available. But I effectively use what I can.