It’s just a number. Minutes are arbitrary. 9 is arbitrary.
Sit. Sit comfortably. Sit still. Don’t get fancy.
Set a timer for 9 minutes.
Open your eyes.
Fail to notice your breath. Continue to fail to notice your breath.
Have no thought.
Notice everything around you. Avoid focusing on anything.
Look straight ahead. Blink. Fail to notice that you blink. Keep looking straight ahead.
Keeping having no thought. When you have a thought, stop having the thought.
Keeping noticing but never focus. Allow noticing to flow.
Time’s up. Turn off the timer. Get up. Move about.
Do this once a day, most days a week.