When I did it, I took off about 5 in the morning and got back around 11 at night....18 hrs. Mine was a lap of Kentucky, with a little bit of WV added to get the required mileage. Since I took off before the sun was up, I headed east for a little bit, then went south at Charleston, WV. By the time the sun was up, I was heading west for the other end of Ky....it is a very loooong state. Was about 6 by the time I headed back east, so sun was on my back while setting. Summer sun in your eyes for hours on end is not fun, so I suggest setting your time/course to avoid that. I used primarily Ky parkways, which are 3-4 land highways with 65-70 mph speed limits, and tried to avoid expressway as much as possible. Did mine over Labor Day Weekend, on a Sunday, to avoid traffic as much as possible and give myself a day of rest before and after. I had plenty of time to take longer rest/gas stops as I wanted. Stopped a cople of times just to stretch and rehydrate. Stopped for 30 minutes for a meal mid-day. It was an EASY ride.
I also did a 850 mile ride as a charity fundraiser, 2 years ago. Took me just about the same time, but it was all 2 lane roads for the first 750 miles. I made it s point in that ride to make sure I enjoyed all the roads I was on, so I went down through eastern Kentucky, crossed over extreme western Virginia, and did a bit of eastern Tennessee, before heading back up through the Danial Boone national forest area of south central Kentucky. I was very tired by the end of this ride, but I found some really really great roads that I had never been on before. I could have stretched it out to a SS1000, but since I had already done one I didnt see the point. I was tired and just wanted to get home...LOL.
Since your starting point is Charleston SC, you have several choices on how to set up your route for an enjoyable ride. Personally, if you are just going after a SS1000, I would suggest a circular route. However, if you want to do it as part of a trip, then pick a destination and head for it...Key West? Texas? Maine? Just remember...if you do 1000 miles out...you still have to do at least that to get back....