In Android 10, there is a new menu “Digital Wellbeing & parental controls”, you can customize the time limit for using the phone so that have a healthy and balanced life. Set daily timers for most apps, when the app timer ends, the app is paused for the rest of the day.
Touch “Settings” from main menu->touch “Digital Wellbeing & parental controls”->touch “Dashboard” (touch “show your data” first if it is the first time to access this setting) -> touch the app which you want to cancel app timer-> touch trash can icon to delete timer.