I've always heard that months 6-9 were the most difficult. In the past, I would relax at about 6 months because that's when I started having the most difficulty detangling new growth. This time around, I didn't seem to have that problem, but I think there are a couple of reasons why. First, I used to stretch for 6 months minimum and did so for about 3 years. I think that prepared me. Second, I started getting my hair texturized instead of relaxed bone straight, so I had less of a difference in texture. Finally, I just decided that I wasn't going to relax anymore and that there was no other option, so started focusing on what worked. I'm just about 13 months post, and I stil get rollersets. In fact, I think it's easier to rollerset now than it was at 6 months because there's just as much natural hair as texturized hair.
But back to your question...I think the key is really deep conditioning at the 6month mark. Not just slapping conditioner in, but making sure to really coating semi-towel dried hair with conditioner. I apply in sections and use a wide tooth comb to detangle. I find that this helped tremendously in the earlier stages, and now I only do it sparingly because my hair is easier to detangle.
Good luck...the good news (I think) is that with a long transition, there is a point where it gets easier and you love the manageable, natural hair.