Timezone change

I find a couriosity,
the raidplaner changes, without me, the timezone and on this he also change the Summer/Wintertime.

The raidplaner works with UTC-Time and on Feb21 the time is changed from UTC+1 to UTC+2.
In Germany the Summertime 2018 starts on March 25 not feb 21 ;)

So the question is - where can i change this setting?