The Winter Semester officially starts on October 1st. Teaching of courses then starts about 2 weeks later and runs until early February, with (in-presence) exams scheduled for the weeks after teaching finishes. There is a starters' week in the first week of October, facilitated by older semester tutors. Highly recommended to take part in order to get to know the University, the city, and other students and to learn the ropes!
The summer semester starts on April 1, with teaching starting on the first Monday in April. Unfortunately, there is no starter week for the summer semester (as only a handful of Master courses allow a summer start).
NOTE: the plan for the summer semester is to have predominantly in-presence, face to face teaching, with only very few exceptions (unless there are new regulations that require us to return to online teaching).