To start a countdown timer, from the watch face, say “Ok Google” to display the "Speak now" prompt. Note: If your watch doesn't respond, tap the screen to wake it up.
Say "Set a timer for <time duration>."
Once you set a timer, you’ll have a new card with the countdown.
To pause the timer, touch the Pause icon.
To resume the timer, touch the Resume icon.
To end the timer, touch the End timer icon.
To reset the timer, touch the Reset icon.
When your timer goes off, dismiss by swiping from left to right on your screen or by pressing the Power button.