The Danube Cycle Path Passau Vienna starts in Passau in Germany and goes to Vienna in Austria. If you cycle an average of around 40 km a day on a cycling holiday, it is 7 days from Passau to Vienna. Unless you take a little more time and take a day off. Maybe you want to stay a day longer where it is particularly nice.
Of course, the route from Passau to Vienna can also be covered in less time. But 7 daily stages are the classic standard. You can enjoy a vacation week with bike daily stages of 40 km. Only from Linz to Grein the stage is a little longer.