Xfinity stream on roku timeout

The app stops after 2 hours. If I watch a long program or movie, the popup "are you still watching" comes up and quickly goes off, turning my show off. If I'm busy or sleeping (I like the noise) it shuts off, eventually going to screensaver. I tried resetting the Roku and the app. There is no setting to adjust for timeout duration. I want it to come on and stay on.