It took us almost 14 hours to Hilton Head from Bethesda two summers ago and we try to drive fast so I feel your pain in needing to break up the trip. There's no way it's 7 hours unless you fly through the middle of the night.
We stayed overnight in Rocky Mount, NC which has absolutely nothing going for it except a cluster of inexpensive hotels. It was supposed to take us 4 hours to get there on a Friday and ended up taking 6, which put us in a foul mood

The area around Stafford, VA alone set us back an hour and was just brutal -- nothing like being an hour from home and then losing another hour, barely chipping away at your trip.
It then took us another 7.5 instead of 5.25 hours from Rocky Mt to Hilton Head (the last hour being in shooting distance of Hilton Head was especially demoralizing. Just so much traffic all trying to disperse onto the island.)
Like others have said, the drive is dreary and nowhere interesting to pull off. You just have to make your peace with it