My first reaction was, "You're kidding me, right?". It doesn't make sense - it's the wrong column. It also doesn't match the documentation. I don't even know how you find out that would work. Anyway, it *kind of* worked. A couple of points:
It set the duration correctly for all but my subtasks. Any idea on why they didn't get set?
It also didn't set ANY of my Planned Hours, just duration.
If using this method (putting the duration unit in the duration type column, how do you set the duration type? (meaning S for Simple, A for Calculated Assignment, etc.) The interesting thing is that for my subtasks, I noticed that the Duration type was set to simple, and the other tasks were set to "Calculated Work". This may be why my subtasks didn't get their Duration set.