If thr goal is to master the skill, then it takes as long as it takes and there shouldn't be a deadline.
If you need to pick this skill up in order to accomplish a certain task, then mastery isn't what's required. This is a challenge we face regularly as software engineers. There is an art in deciding which rabbit holes to plunge down and which to step over.
My process for doing so is roughly to survey the field in a broad and shallow manner to understand the context, evaluate what parts of it are most relevant to the matter at hand, and then study them in depth. But try to keep it tethered to the task you set out to accomplish. The minimum amount of information you'll need to capture is probably still a lot, so don't put more on your plate than you can eat.