What are the working hours for full time PhD students in Germany? What are the working hours per week for full time PhD students in Germany? Also, how many holidays are granted in a year? How is the work-life balance for full time PhD students? Thanks!
You are typically paid for 50 or 65% to do work on some project, but that just means that the university graciously allows you to write your dissertation unpaid in the remaining 50 or 35%.

How much you really spent is hugely dependent on the discipline, the department, the advisor, and yourself. The best case scenario would be when there is a huge overlap between the project and your dissertation, both the department and the advisor are very supportive, and you are very disciplined and get a lot of work done in a short period of time. This does happen, but not everybody is that lucky.