All international students are highly encouraged to apply during the First (main) admission round. This round takes place many months before the start of a semester and gives students the time they need to pay their tuition fees, apply for and receive their residence permit (if required), find housing, etc.
The Second admission round is an alternative for students from EU/EEA countries as they do not need a residence permit. Non-EU/EEA students will most likely not have enough time to obtain their permit before the start of the semester.
However, even EU/EEA students are advised to apply during the First admission round, as some programmes can be applied for only in the First round. Also, this provides applicants with an admission decision much earlier, which is helpful in making decisions about their studies.