Before you start a task, write down what you think it'll take. Then time yourself. Then look at the difference.
That's it. That's the whole habit. The first week is humbling. Things take twice as long. Other things take half as long. There's no pattern at first — just a lot of "oh." That oh is doing the work. Your nervous system is recalibrating around real numbers.
Within a couple weeks, you'll start guessing better. Not perfect — just less wrong. You'll naturally pad emails by 20% because emails always run long. You'll know that "quick errand" means 45 minutes, not 15. You'll stop overcommitting your mornings because you've seen the receipts.
The trick is keeping the habit small. Don't estimate every task. Don't track minutes. Just notice. The act of guessing-then-measuring is what teaches you. The data is a side effect.
A blob in your corner doesn't hurt either.
