It’s worth bearing in mind that, as a rule, one language level is achieved per German course. On average, a language course lasts three months, with one to two sessions per week. However, the duration may vary depending on the course format.
If, for example, it is an intensive course, you can either reach the same language level in a shorter time, or achieve a higher language level in the same amount of time than you would with a regular German course.
The duration of the German course therefore depends on the course format, the frequency of the sessions and the target language level.
It’s best to consider what level of German you’d like to reach by when, and how much time you have available (work, university, etc.), and then look for the German course that best suits your daily routine.