"I can't stand waiting around"
We've come to what I think is the belief underneath the others. If you leave enough time to be sure of arriving on time, then most days you'll arrive early, and you'll have to wait. Waiting is dead time. You'd rather spend it doing something.
I want to grant the first part. If you plan to be on time on the bad days, you'll be early on the good days. There's no way round that, and anyone who tells you that you can be exactly on time every day is selling something. The question is what the early minutes are worth, and what the late ones cost, and I think the habit has priced both wrongly.
Consider what you're comparing. On one side is ten minutes in a corridor before a meeting, or in the car outside a friend's house, or on a bench outside the dentist. On the other side is the dash, the apology, the chair by the door, and the first ten minutes of the meeting spent catching up on what you missed. You've treated the first as pure waste and the second as roughly free. Look at them again. The ten early minutes are yours. You can read, think, look at the trees, or send the email, which is now a thing you're doing while early rather than a thing that makes you late. The ten late minutes belong to nobody. You aren't working, because you're walking fast. You aren't in the meeting, because you haven't arrived. And the people who are in the meeting are now partly waiting for you.
There's also the matter of what an appointment is. When you agree to be somewhere at nine, you've made a small promise. Being early is the price of keeping it reliably, because time is uncertain and the only way to be sure of not being late is to aim early. Someone who refuses to pay that price isn't avoiding waste. They're passing the wait to the other person. On Thursday, Dan and Ellie waited twenty-five minutes for you. You didn't wait at all. The waiting happened. It just happened to them.
Some of the dislike of waiting is about what it seems to say. Being early can feel like being the keen one, the one with nothing better to do. I'd suggest that this is a picture from school, and that most adults don't see it that way at all. From the outside, the person who's there at five to nine with a coffee looks calm and ready. The person who arrives at eight minutes past looks harassed.
If you can accept that early minutes aren't waste, the whole habit becomes easier to give up, because the reason for cutting it fine disappears. Chapter 18 is about what to do with those minutes, and it may turn out that you come to like them. But I don't need you to like them. I only need you to see that they cost less than the alternative.