Rule Number Three: Time is never what you think – be early or be ready to be late.

If I have one talent that serves me well, it’s my ability to judge down to the minute exactly how much time some action will require. Many people – most, perhaps – do not have an accurate concept of time.
If you can’t tell me how much time it takes you to lock your door in the morning on the way to work, you’re probably one of those people. So, any time you think about saying “Sure, give me 20 minutes,” just add 5 minutes. Scale as needed, and you’ll find fewer people waiting on you, less stress in your day, and more time to get it right.