I think there is a difference between > length of the critical path and > six months is as fast as it can get done unless "length of the critical path" acco

I think there is a difference between > length of the critical path and > six months is as fast as it can get done unless "length of the critical path" accounts for the quadratic(ish) increase in communication overhead as you add more people. I think that is a little unclear from the question: is the length of the critical path the sum of times one person would take to do those tasks or the sum of the times an overhead-laden person would take to do those tasks?