Well, it depends on you, what type of learner are you, whether you are a slow-learner or fast-learner and your availability and depends on a whole lot of factors. If you are serious about getting into the BI industry, with the right skill set, then I would recommend you to enroll in a good Power BI certification course, from Intellipaat. This course helps you to build your practical skills that will ultimately help in enhancing your practical skills. Generally speaking, it would take you at least a month or two to get yourself trained, and 6 months to master it fully. If you wish to get started, then do so by watching the following video on Power BI Training.