It's possible to set up time schedules of when devices no longer should be be able to use the internet. 

This is done by navigating to Parental control, and then setting up the rules.

Link to big picture

It's important to note that during the start and stop time, the device will loose all connectivity. In the above example, the internet would stop working for the device at 23:00 (11PM) every weekday, and start working again at 08:00 (8 AM).

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