I think the reply above covers it pretty well, but I just had to reply because I'm also a neuropsychologist and there aren't that many of us!

It does come down to the mania vs hypomania question, nothing to do with duration. But it could well be that one pdoc will diagnose mania and another hypomania in the same patient. There are the clear cut examples of each, but the middle area is grey. For example I think I'm currently hypomanic, but pretty sure my pdoc thinks manic.