I'm a little over 15 months post-relaxer and I STILL don't make puffs on shrunken hair. I make puffs all the time on hair that has been stretched with a braidout or twistout, but my hair shrinks way too much for my liking now to make a puff that doesn't look pathetic or remind me of a boy. (I know that might sound crazy but when I was younger, like in middle school, a lot of boys used to take their cornrows out and put their hair in these semi-puff things until they could get their hair redone, so that's what I would think of every time I'd try to do it with full shrinkage... so I realize it might be okay to someone else but to me, I can't get that masculine image out of my head)
I made a cute side puff on an old braidout that I liked at about 12.5 months post (it's in my LHCF Au Naturale album if you want to see), so my hair was around 6-7 inches or so. I think that is the minimum for me, even on stretched hair, but I also realize that people with thicker hair can pull off a puff on shorter hair. I need the length because I don't have the thickness.