How many hours each level takes
It is easier to measure the timeline in practice hours than in months: months depend on how often you study, while the volume of material per level stays stable. On the CEFR scale and in our experience one level takes about 100–150 hours of quality practice, and that includes not only the lesson but the homework between sessions.
Lower levels come a little faster, higher ones need more time to consolidate. Approximate volumes: reaching A1 from zero is around 90–120 hours, A2 adds 100–130, B1 another 110–150, B2 plus 120–160, C1 about 130–170 hours. So the path from zero to B2, which opens up work and study in English, adds up to roughly 500–600 hours.
Turning hours into months is simple: multiply your lessons per week by one and a half hours of work (lesson plus homework) and divide the target volume by that weekly pace. That is exactly what the calculator above does, showing a range from the optimistic to the steady scenario.