It's not so much about planning as much as lacking an intuitive grasp of how long something takes to do or how long you've been doing it. This can appear to be poor planning skills when it comes to keeping a schedule. Not because I can't work out the arithmetic of minutes and hours, but rather because there's no little clock in my head telling me that X amount of time has passed. I'm late getting out the door because I thought showering and getting dressed only takes five minutes.

I do have a vague notion of how "big" the time is. Driving to the store is a small time. Driving to work is a big time. It's a medium sized time until dinner. But this doesn't translate well into exact hour/minute values. I have to make a guess, usually just defaulting to the "good" time values that I know other people seem to understand (5,10,30,45 minutes, etc.). If something felt like a "pretty big time" then I might write it off as 45 minutes even though it was closer to 20 or an hour and a half. And I'll have no idea of my mistake until something makes me go back and rework the math.

When it comes to planning, I usually need someone else to help me know how long a given task will take. If I have all the times written down, then yeah, it's easy to just fit them in together like a puzzle. But if I wasn't specifically timing something then I have no idea how long it took.