If you're seeing nest there has to be squirrels there. I don't typically sit much, I still hunt. Slowly move, and I mean SLOWLY through the areas where you know squirrels are at. I usually will see them moving in front of me, and then plan my moves from there to get a shot on them. If you're sitting a half hour should be enough time for them to come out. Are you hunting during active times of the day? I don't know what time that'd be down there but here in Ohio the best time right now is from eleven till three.
-Jake