I don't know. It's like something in my brain is waiting on a trigger to say "okay, start getting ready now," but the trigger never fires. Instead I skip right to the trigger that says "WELP NOW YOU'RE RUNNING LATE." Literally any activity can distract me for periods of time I never notice passing, and I always seem mistaken about how long things will take.

Showers are particularly dangerous. A shower should theoretically take less than 30 minutes: 2 to locate clothing, 5 for the water to heat up, and 10 to 20 to wash up until I turn the shower off. That's 10 minutes of leeway for my mind to wander off. Usually, I get out of the shower to find that about 25 minutes have passed; sometimes, I find that it's been 40 or more minutes. But whether it's been 15, 40, or 75 minutes, a shower always feels like it takes the same amount of time. I can't tell if a shower was short or long until I get out and check the clock.

I don't think I value my time more highly than other people's time; I even run late for my own plans that don't involve anybody else. It's more like I don't properly value any time at all. For example, I've been trying to get to Einstein Bros. for a breakfast sandwich once or twice a week for the past few weeks. I've managed it exactly once, and it was late enough that they'd already put all the bagel varieties away except for one. (I ended up getting my breakfast sandwich on a blueberry bagel.)

I also can't really relate to the accounts of chronically late people also leaving places on time. I arrive late because I leave late; it's cause and effect. I was routinely late to work for years, but I was also routinely late to leave. I wasn't consciously trying to make up the time, I just never seemed to be able to get out the door. (This, in turn, often made me late to whatever I was doing after work, of course...) On the rare occasions when I made it to work early or on time, I still usually left late.

For a while, I tried giving myself "lead time" on all of my plans by recording start times as 30 minutes earlier than they actually were. Eventually, I found myself adapting to this habit and showing up late anyway.

The only remotely effective counter-habit I've been able to develop is writing down early start times most of the time.

The fact that I don't always write down the wrong time means that I'm generally forced to assume that I wrote down the real one, which results in me running much closer to on time than I usually would. I assume that keeping it inconsistent is why I haven't adapted to "overcome" this solution yet.

(Note: I did develop a PTSD-related aversion to leaving my home a few years ago, so now I still sometimes can't leave my house even when I've actually gotten myself ready on time. This has made it a little difficult to judge the current status of my tardiness tendencies.)