, no more than twice a day, if even twice. Most tanks will do plenty well if you feed once a day. (I say that because most fish food labels say three times a day) It reduces waste, for one thing. Even if you think the fish are hungry later, remember that fish are ALWAYS hungry!
They'll always try to eat, unless they're absolutely stuffed. And there's no reason for them to be so stuffed. Another thing to factor in depends on yuor type of fish- what do you have?