I honestly never noticed I was scheduling my time in half-days or even full days, but it's so true for myself. I would've thought it was some sort of anxiety thing, but having plans several hours away in my schedule is extremely debilitating to my creative flow. Just one scheduled item, even something enjoyable like going out to a nice restaurant, can practically paralyze me from working on stuff. Fortunately chores, errands, and house work generally do not fit this bill.
Or rather it prevents me from venturing into the unknown, like when working on a novel program or writing music from scratch. I really had no problem accomplishing day-job things despite knowing I had scheduled meetings later on in the day.