Plan rest stops along a route.
Rest stops are planned by distance rather than by time because service areas exist at fixed points on a route, and 100 to 120 miles is both the conventional interval and roughly two hours at highway speed. The stop count is one fewer than the number of legs — you do not stop on arrival — which is the arithmetic people most often get wrong when planning a long drive. A 480 mile route at 120 mile intervals is four legs and three stops. At 20 minutes each, that is an hour added to a 7.7 hour drive. Twenty minutes is a realistic figure once fuel, a queue for the toilets and a coffee are included; ten minutes is optimistic.
Rest Stop Planner
Legs = route miles / miles between stops, rounded up; stops = legs - 1; total trip hours = route miles / average speed + stops x stop minutes / 60
Three or four at 120-mile intervals. That adds roughly an hour to the journey, so plan arrival on total trip time rather than driving time.
Distance is easier to plan around real service areas, but check the interval in hours too. In heavy traffic 120 miles can be three hours, which is too long between breaks.