Yes. When you connect Roku to the router, you’ll see the Roku device in the status page. Save the device with a name so that you can identify it in parental controls. In parental control, create a profile for the Roku device then add a Calendar (with empty domains list) to it. Set allowed time slots in the Calendar.
Since the Roku box has both wired and wireless connections, you’ll need to identify it both ways. So the profile you set up for Roku will list two devices, let’s say roku-wired and roku-wireless.