That is the question. I'm debating that on these Jinx socks when I go to do the heels. I'm planning on just doing the Granny heel, then doing each heel separately after the socks are done. I'll use scrap yarn when I think my leg is long enough, which will mark the stitches for the heel, then use the same yarn to make the heel.
However, I got to thinking that when I go to do the heel, my gauge will change because I'll no longer be doing both socks at the same time. It will likely be tighter, which will make a smaller heel, so I'll likely go up a needle size to compensate. Nothing like a handmade sock with an ill-fitting heel.