On the ring around the outside, where there are some sticky-out bits and some pressed-in bits, that's what sets the on / off times.
Pushed-in=on, and pulled-out=off, usually.
But it may be the reverse: looking at the existing on/off settings, I suspect it may be.
It looks like a 7-day timer.
The markings show 7 segments, I thru VII, each one representing a day.
The days are labelled in various language abbreviations.
Each 24-hour period has 12 tabs, each one representing a 2-hour period.
The entire ring will rotate, doing one complete revolution in a week.
So you can set the on/off times differently for each day of the week.
So for example, looking at sector VI (Saturday ), it will be on ( or off! ) from about 08:00 till about 16:00.
The entire ring can be rotated to set it to the current time, as indicated by the rotaty-arrows.
There will be a mark somewhere on the main body ( possibly obscured in the photo, near the 'apt' logo? ) which indicates the current time and day. Twist the whole shebang in the direction indicated by the arrows till the current day / time lines up with this mark.
