macOS High Sierra
Set a sleep timer
You can set DVD Player to automatically stop playing a movie after a certain amount of time.
Set the playback timer: Choose Controls > Timer > Set Timer. Choose an action and a timer duration, then click OK to start the countdown.
Show the timer countdown: Choose Controls > Timer > Display Timer.
Pause the timer: Choose Controls > Timer > Pause.
Turn off the timer: Choose Controls > Timer > Cancel Timer.