If you put in 20 good, quality hours per week, that should be plenty and you shouldn't even need to take off those whole weeks.
Just got my score back from taking AUD in May and passed with an 85. I put in 60-70 good hours, tops (that includes the 16 hours or so of just watching lecture). I didn't do well on Becker homework (1st time through) and the one practice exam I took was not passing material. I figured maybe a 65 or so if I didn't pass and at max an 82 if I did pass. I thought my exam was not too difficult, but I wasn't sure if it was because I had questions I knew or was just doing bad and never getting the hard testlets (I still question whether they are truly adaptive). However, the simulations seemed relatively easy, with one exception.
Even though I do strictly governmental/non-profit auditing, the style of this exam is the hardest for me because of not having numbers, for the most part. There is a little memorization of things like mentioned above.
As a comparison, I had old 2010 materials for BEC in February. I didn't review anything on corporate governance until the day of the exam for 30-45 minutes (and I was comparable, not even weaker in the MC), didn't know exactly how the IT stuff had changed (just that it did) and had nothing on any type of new international related questions. I studied maybe 40 hours for it and passed it with an 85 as well. So, it would seem AUD is harder by that, but as I said, AUD is just not my best style of test to take. But the person who thinks it is the easiest may have it be the perfect style of test for them. Other than the amount of material in each of these sections, I think that is that is the biggest factor in the difficulty of the particular section.
BEC - 85
AUD - 85
REG - 76
FAR - 82