You don't have to do it until week 13 if you don't want to. I don't think it's even called AAMW any more unless you're a CD dinosaur (like me!) it's now a week of 810. I find it boosts my weight loss as it shakes up your motabolisum (I can't spell! lol) a little bit.
HTH.
Some stay in ketosis and some don't at 810 (it's a suck it and see senario).
Strangly enough I tend to lose more weight on my AAMW than I do on ss weeks (but then I'm a bit of a freak of nature on this diet!).
I do the Dutch version of CD and I "AAM" every 4th week. I do not get out of ketosis and I still lose it just seems 'slower' because I'm filling myself up