Make sure that your YouTube app is up to date, because of this feature only available on 13. 17+ version. If it’s not, go to the Google Play Store or App Store and update your app.
If you are an iOS user, just skip to the next step.
You can also get to this Menu by clicking your profile picture and then Time watched.
When you are done, go back to the normal window and enjoy your favourite videos. When the alert shows up, your video will pause until you dismiss it or resume playing the video.
Alternatively, navigate to Settings > General > Remind me to take a break to manage the reminder.