Socks and Pumpkins

We went to a pumpkin patch on Sauvie Island on Friday and it was so much fun! We got lots of cool pumpkins, went through a hay bale maze and saw cute farm animals. They have a big corn maze too but we're waiting to go through it with some friends next week when it's haunted. Bradley was very well behaved at the pumpkin patch (except for peeing on a pumpkin) and he liked sitting in the pumpkin cart.
I'm plugging away on my dublin bay socks. So far, my 1st sock is almost 7 inches long. This being my first pair of socks, I'm not sure when to stop. How long do you like your socks? I'm using Lorna's Laces sock yarn and I don't know exactly how much they'll stretch lengthwise when they're on and I'm knitting them for my mother-in-law so it's not like I can try them on and knit until they fit me well. How long should I knit it before starting the heel? Advice is appreciated.