My twins eat every three hours and then I keep them up for activities and put them for nap at the end of an hour and 1/2. That tires them out and they sleep for the next hour and 1/2, til it's time to eat again.
So, they nap six hours a day, unless I am able to keep them up throughout the entire last three hours before bed, in which case- 4 1/2 hrs.