How hard is it and how long to study?
It is as hard as you are unwilling to study & learn.
Study as long as it takes to feel like each question is INSULTING you just for ASKING it.
I took the 24, which I can only assume is similar in degree of difficulty, and did not find it all that tough...probably not as hard as the 7 in reality, although the material was much more boring. Spent perhaps 40 hours studying and scored 80%.