Hi Pclan5,

A lot of people have been wondering why there is such a long wait on the mastery challenges. The reason for this is because Khan Academy wants you to retain the information being taught, so you will not just learn it once and forget about it later. This is important because most of the skills rely on knowledge learned in previous lessons. While it seems like a pain, it will probably help you out in the long run. 

If you are trying to do mastery challenges to get badges and unlock avatars, try doing some of the practice challenges. You can still win the Geek of the week: practice Moon badge if you complete 5 practice tasks in a week. In the meantime, try aiming to get some of the other badges like Picking Up Steam (Meteorite badge), Nice Streak (Meteorite badge), Going Transonic (Moon badge), Going Supersonic (Moon badge), and Sub-Light Speed (Earth badge).That way, you will be all set to master the skills when the wait time is over :)

Hope this helps! If you have any other questions, please let me know.

tAG54