While I have managed to bring a young and gifted woman to level B2 within three months (see video below) and believe that we could also have achieved that in just two months, the average learner will most likely need anything between one and two years to get to B2 and about six months to get to B1.
While your progress depends on quite a few factors (age, intelligence, knowledge, education, motivation, living situation, to name just a few) it is mainly determined by the quality and amount of work you invest in to reach your goal. If you invest only 30 minutes daily in your German learning, you will certainly need longer to achieve your goal than if you invested 4.5 hours daily (like they do in an intensive German course, for example.)
The problem is that you most likely will have to work in addition to your German learning and those 4.5 hours of studying are quite exhausting and difficult to fit into your daily schedule.
Make sure to set realistic goals and to adapt them according to your working and living conditions. The learning cycle that you find in this book will help you fit your German learning into your day as it can be separated into 20–30-minute pieces, which is much easier than finding 90 minutes in an eight-hour workday.
Also try to explain in your own words what you have learned in this lesson.