Wow tough call. Seeing that you need to be in Boston at a specific time, I would map out a place or three that you really wanted see, get to them in a reasonable amount of time and relax. You're probably looking at 1,000 miles from Charleston to Boston.
I travel 95 through MD, DE, NJ, NY, CT, RI and finally MA (20 mi south of Boston) a few times a year - and every trip is different as far as traffic goes. I can generally make the 450+- mile trip to the grandkids in Bowie, MD in about 8 hrs, driving all interstate at about 70 mph, normal traffic, no sight seeing and in a C6 or mini van. If I were driving (450 miles) back roads, sight seeing, maybe taking a ferry and etc - I would plan on 2 - 3 days. You can easily kill a day driving along the RI coast, going to Newport, etc and still be 1 1/2 hrs from Boston.
Good luck in your planning, if I can help just yell!
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