Also could be your brain saying "Ok I have enough input data, now let me do some backend processing subconsciously while you do more mundane stuff" and then 3 hours later what has to be done makes way more sense. I find sometimes that constantly nagging myself to keep working/stay on task is self-defeating in this way. I like to do "cron" stuff in the morning while my brain gets fully online like, walk, work out, any scheduled task that is basically no brainer and needs to be done. Once I get all that out of the way then I focus on projects and other activities that require more deliberate and profound thought. I think someone else commented in this thread that "setting the cadence" for the day like this is important to be productive but I try not to be so grind-y in the afternoons because I know my brain is chugging away on its own. YMMV