It took around 1 month until I got a reply from them. The team first contacted me to set up a day for the interview and then I got an Email from HR department. And it was one interview in total, I had to go to Düsseldorf and had the interview directly with the team. The interview questions were not very hard to answer, if you know the accounting stuff. In my team they dealt a lot with the cost structure, so preparing for cost accounting part is rather important in this case