the Autumn semester of the 2016/17 academic year will start on 5 September (Monday). The exchange students should arrive the previous weekend (around 2 September).
The exam period starts in early December (depending on the faculty), and the students can finish with their exams before Christmas. But it really depends on how many exams they have and how fast they want to finish. The last day of the exam period will be around 20 January (Friday).
The Spring semester will start on 6 February (Monday) and the exchange students for the second semester should arrive around 3 February. The exam period will start in the second or third week of May (depends on the faculty) and lasts until mid June. However most of the exchange students usually done with their exams in May or in the first days of June.