during covid I was "overemployed" at first 2 jobs, then 3 (which I sustained for over 8 months). Some of it was luck, like not having conflicting meetings, having jobs in different timezones, and the leniency given due to the chaos of the times, but I actually did get work done. But during the average day, I was only there to respond to slack and participate in meetings. I wouldn't really "work" as in write code, until after the sun went down (and I was west-coast working a central time job). I was just a body in a seat until the day was over, then once I knew nobody was available to pester me or expect me to do something, I could crack open the editor and hyperfocus. I also found that getting up super early, I could hyperfocus for an hour or 2 in the AM, then about 9-10am once all the meetings and bs started, I was just an actor. The rest of the time was juggling tasks and procrastinating, and using that energy to drive me to get work done. I would work saturday and sunday mornings (often, not always), but once my focus was lost I would stop. It was a hell of a time, but I learned that (like you) certain times of the day just weren't compatible with getting anything done. I dont think it's correct to say its due to "overstimulation" or caffeine, I think it has to do with brain states, and somehow knowing that I had to be available on slack (or had to make sure my mouse jiggler kept my status green) seemed to be enough to break me away from writing code.