I have type 4b hair like some of you ladies here, and I've just started stretching my hair for more than 7 weeks. Before finding this forum I used to relax every 6 weeks approximately.
But now...I can stretch to 14 weeks! 14 weeks is the longest I've gone. But keep in mind, that my hair (although it's 4b) is very baby fine naturally. I don't know how it would be if my hair were really THICK. I long for thicker hair, so tha'ts why I started stretching my relaxers. I even switched to a mild relaxer, and that has helped TREMENDOUSLY! I found it easier to stretch when I had a mild relaxer than when I had a regular strength relaxer because the contrast between mild relaxed hair and virgin hair isn't as GREAT as regular strength relaxed hair and virgin hair.
The only reason why I stretch my relaxers so long is so that my hair can be thicker, and I can minimize any chance for overlapping of the relaxer.
The first time I stretched, it was MURDER! But the second time, I got better at it. I think it gets easier everytime you stretch. 8 weeks is a breeze to me, but @ 10 weeks it starts getting harder and harder. At 12 weeks, it can feel like torture sometimes! LOL* So, maybe the best thing to do is try to stretch longer than you would usually go at least twice, and see the condition of your hair. If you think your hair is better off stretching, then continue on. IF you don't, then you should just go back to your usual routine of relaxing.
Bottom line: Just do what's best for you and your hair.
ALso, some factors that might influence your ability to stretch relaxers...
-the relaxer type
-the relaxer strength
-how thick your hair is
I usually try to do as little manipulation with my hair as possible while I stretch. Dominican roller sets help me out a LOT while stretching! I go every 2 weeks. When I don't go, I wash my hair and deep condition every time. Believe it or not, but washing your hair in the shower does WONDERS for the detangling process!
Good Luck!