Hello,
Server time is CET (which is almost always GMT+1).
Hope this will help :/.
To be more precise :
Winter CET :
Time zone offset: UTC + 1 hour
CET is 1 hour ahead of Coordinated Universal Time (UTC)
Note that most places observe daylight saving time/summer time during summer, and are therefore using CEST instead in the summer. See below for details.
Summer CEST (from end of March to October)
Time zone offset: UTC + 2 hours
CEST is 2 hours ahead of Coordinated Universal Time (UTC)
Note that CEST is a daylight saving time/summer time zone. It is generally only used during the summer in the places listed below, during the winter CET is used instead
I played on *far away* servers for other games in the past. Time zone offset is something you get used to, when you know what is the server time

.
I thought that the calendar shows you exact event's time depending on your time, not server time ?
Good luck to teach your guildmates about time zones !