Trip Time Difference

This is not a problem for me but I figured someone like Steve knew the answer. The trip time for a 576 mile trip shows 9 hrs and 12 min in BaseCamp. BaseCamp is set to 0 for Custom Speed Adjustments. The total trip time for the Nuvi 3597 is 10 hrs 5 min. I do not see a preference on the Nuvi to adjust speed. The route is not recalculated and the route is the same on the Nuvi as BaseCamp. Does anyone know why the total time is different? Thanks