You might hear: "Just one more level," "I am almost done," "This is the best part." What you are seeing is a child in a highly activated neurological state, with dopamine flowing and the reward system fully engaged. Screens, especially games, are designed to be almost impossible to stop at any natural breakpoint. The resistance to stopping is biological, not willful defiance.
I hear you, and I know it is hard to stop. The timer says it is time, so let's find a good stopping spot right now.