We got exactly the same problem, since December 2016!
All events (50.000+ in our case) are delayed with "1 hour". If you click on the event, the filled mask will show the correct time scale but in calendar view, all events are delayed
The whole groupoffice system is gettin unusable
Timezone is GMT+1 & servertime is correct.
In earlier versions of groupoffice (3.x, 4.x & 5.x) we got no problems over the last 6 years. No everything goes nutz