I have camped in 4 of the east coast NF ( Va, WV, Tn and Ga) and several state forests. I have never had an issue running to town or leaving all day for day trips. My last stay in the Cherokee NF in Tn, the guy next to me very obviously left for work and came back in the evening. So, to the best of my knowledge, there are no specific rules against it, though you DO have to stay on the site the first 24 hrs. After that, come and go as you please. ( the 24 hr rule is supposed to cut down on people picking out the choicest spots on Tues, setting up, and comming back on fri to camp for the weekend) , and of course, the 14 day stay rule to give everyone a chance, and to let the sites " heal " from overuse. Truth is, I know people who have camped 3 weeks or more at the same site as long as they kept low key, and have heard of someone ( second hand info, take it with a grain of salt) who spent 6 months at a dispersed site.