Or it could be that you had a brilliant idea for the rest of the sentence, but the strict rule prevents you from writing it down, and next day you can't remember it and chase it all day and still be unsatisfied in the end. Either because of lost time or because you couldn't remember/recreate it, or even both.

I suppose it just goes both ways. Try not to finish sth so that you don't have the somewhat hard task to start with sth new next day. But at the same time don't stop in the middle of sth that's difficult to pick up from. A strict timing rule does only help if you are statistically more often at a point where it's easy to pick up again. I doubt that you are though, so I'd try a more concious approach than a clock.

I really like the parking downhill analogy.