Thank you JRMumma !
I can also explain the "bet they are never late for work/a plane" issue.
For work every day, I'd have 'time splits' - I didn't think each day about what I had to do to be at work for a set time, I'd think about me leaving the house and what I had to do for each task. It would be the same every morning, shower, dress, do my hair, do my make up, get my bag/shoes/coat, leave the house, walk to the train station. i'd get up at the same time every day, I'd have points to make it clear I'd spent more time on each job (eg. I had to be out of the shower by a set time. I needed to be finishing my hair and doing my makeup by the 7:30am news on the radio, when I passed a certain house on the way to the station, I'd check my watch and know if I had enough time to make the train or not, or if it was close I needed to walk faster).
However, on other days, I didn't have that, I also on other days have other things to do other than just get out of the house which would make me late.
This is why the woman up thread can be on time for pre-school at 9am but not a toddler group at 10:30am - because I bet before the 9am pre-school all you do is get everyone up, breakfasted and dressed and go (or do other regular jobs you do every day), for the 10:30am one, you add in extra jobs which I am certain if you are a regular late person, you will underestimate how long they take.
Spend some time this weekend, first write down how long you think it takes to do certain tasks like unload the dishwasher, mopping the kitchen floor, put on a wash load (don't just count the time putting the stuff in the machine and switching it on, go from standing in your kitchen, thinking about it, walking upstairs, sorting out a load, going downstairs again and then putting it in the machine), then once you've got your estimates, time yourself. Plus time yourself from the point you say "come on, let's get going" to having all DCs and yourself in the car and backing off the drive.
Learn to allow enough time for how long things actually take, not how long you'd like them to take.
Then add 10 minutes. 