Your Voxy units are flexible, so you won't "finish" them in any specific time. Depending on your needs, your units may last three months, six months, or a year. In that time, you can do as many units and lessons as you need to.
We recommend that you complete 6-13 lessons per week depending on your level in order to improve. If you follow the recommended practice time described in your study plan, you should be able to move to the next level.