Good question. I just did the Sheppard are prep for the MCI (Military Comp Instructor) test a few weeks ago. Initially I worked on it while I had a few minutes here and there in the middle of other things. That's not the way to get it done so I buckled down and worked on it for real for an hour or two a night for a couple of nights in a row. I followed the provided guidance and felt I was ready before I expected, so left it alone for most of a week. Didn't want to peak early you know... The day before the test I did a second practice test, scored less than the first one. I got a 98 on the real test which I completed in about 20 minutes.
The MCI is a much smaller question base than the ATP, I'm interested to hear how many hours guys are putting in on it. Sounds like UnBeatenPath had an experience with it about like what I would expect.