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It isn’t about mastery; but practice and improvement. Most people start with the 30 days to play (it sounds like you have been playing awhile though); then some of the skill courses (such as Your Next Six Chords, or such as you mentioned, the 5 day blues challenge). When you start the meat of the program; the daily challenges: each day Monday through Friday is dedicated to a specific technique. Each week you work on the same technique on that day but with different material from week to week. You are not doing them to master them; but to play as best you can (at least 10 minutes, probably more for many people); and move on; day by day to finish the challenge for the week.
It is establishing a routine; getting your fingers in shape; getting familiar with some guitar information (understanding the physical layout of the guitar and some guitar theory); and playing (no matter how good you feel about it at this point; there are beginners doing the daily challenges as well as more seasoned players). Some challenges will be more challenging (feeling over your head), others more encouraging. You will forget things (I will be 72 in a month, having started in TAC 4 years ago). The more you play, day by day, incrementally, you will be making progress. Some of the challenges repeat, and you will see how the next time through you are better at it. The information will come around again, and you will begin to understand it more, and retain more with repetition. It is a process. It works. Your aim each week with the daily challenges is to complete them (even when you feel you fell short in a week; which I have on many occasions). Keep going!