When not in a ride, or a ride is paused, the Dash will enter a sleep state after a period of inactivity. To awaken the Dash, press any button.
Options for sleep time are:
The Dash will stay in sleep mode for up to 3 hours before powering off. After 3 hours, any unsaved ride data will be saved automatically.
To update your sleep time preference, go to: Main Menu > Settings > Sleep.