As promised, the final result is here. I love it, Have fun, Stefan

I am using a “dual” solution: I do use a PIR sensor together with the MMM-PIR module to switch the monitor to standby via HDMI off. Since the Raspi and the monitor are still consuming energy, I thought about when I do really use my MagicMirror. So I came to the conclusion that I never use and need my MM during night and during my working hours in the week. So I bought a rather cheap clock timer with the capability to program it per day. Every day the MM is switched completely off during night time and every work day during my work time. In order to prevent any potential SD card failure I do use the module MMM-Scheduler to shut down the Raspi well in advance before power is cut. If there is interest I can post the configuration of MMM-Scheduler.

@mpires
Here is the configuration:

                {
                module: 'MMM-ModuleScheduler',
                config: {
                notification_schedule: [
                                // TURN THE MONITOR/SCREEN OFF AT 8:30 EVERY WEEK DAY
                                {notification: 'REMOTE_ACTION', schedule: '30 8 * * MON-FRI', payload: {action: "SHUTDOWN"}},
                                // TURN THE MONITOR/SCREEN OFF AT 23:30 EVERY DAY
                                {notification: 'REMOTE_ACTION', schedule: '30 23 * * *', payload: {action: "SHUTDOWN"}},
                            ]
                         }
                },

The clock timer is programmed to kill the power supply 15 min later than the shutdown time(s).