UPDATE: So, I finished my first challenge. I need to add a few things to it, which will take about 1 hour, which is why I say 70% done. BUT, if I plan on making a second challenge, it's only 45% done.
So, when I had about 45% of the first challenge done, I had a player try to do the challenge. With time penalties (Oh yeah!) and such, it took him about 1 hour to get through. Pretty fun.