We split it up, visiting my sister in Richmond for a night, so left Philly at 10:30am, got to her place by 3:30 (no mean feat with a 5 and 2 year old who need bathroom breaks). We left Richmond at 9:30am and got to Savannah around 5:30/6pm (stopped in Selma, NC for lunch, even driving a half mile to a playground/park to eat in). Left Savannah around 10, stopped for lunch at the rest area just south of Jacksonville (we packed some fruit and the like) and were crossing under the sign at 2:35pm. These were middle of the week.
Coming back, we left WDW on Saturday the 18th around 11:30am, and made it to Fayetteville, NC around 8:30pm (woulda been earlier but the little guy got sick and we had to stop for a bit to let him get some crackers and just not move for a bit). Left Fayetteville around 9:30, reached my sister's in Richmond around 12:45. Left her place around 2:30, nasty traffic north of Richmond, took 301 back for quite some way, got back to Philly a little after 8 on Sunday night.
I'm not a 14 hour drive all at once guy, and my kids won't do it. We didn't think it was bad in terms of masks or traffic on the way down. On the way back up, I'm assuming since it was a weekend that is why we saw so many more people, and I'd say masks were at 50%, and even most of those were just mouth guards. We really noticed it when we stopped at a truck stop on I4 40 minutes after leaving WDW (5 year olds!!!!) and none of them were wearing one, nor were any of the other cars that pulled over (we seemed to start a trend, as 5 cars pulled off too and almost all had little kids who needed to go). I-4 is a construction mess for the 15-20 miles closest to WDW. Also, I-Exit may be a game changer in terms of apps for parents. We were prepared for bathrooms, rest stops, food places, everything.