I have often thought that when people complain of being short of time, it is more often that they are short of brain space. If you do an audit of every minute in your day, there are often plenty of minutes that are ‘unproductive’ if regarded from the outside. But, from the inside, you can’t make use of those minutes for anything very much because it just takes too much energy to upload something productive into your head for a brief time, and then - just when you’ve got going - dump it out again for something else.
This is of course that standard wisdom about why multitasking is inefficient - there are frictional costs of attention involved in every switch, so switch often enough and you get nothing done. Multitasking still has its place, I’d say, but only with routine tasks that you have at the tip of your brain anyway. I quite like the definition that multitasking is a technique for avoiding several dull tasks by doing them all at once.