My Nepenthes are in a large terrarium. I feed them and water at the same time once a week. I give mealworms to maybe half the traps of both my large sprawling N. khasiana x ventricosa and N. ampullaria. For my younger Neps I give them just 1 mealworm.
I have also noticed that once seedlings get to the size where they can take an ant, fruitfly, or baby mealworm that it really helps the growth - with traps doubling or tripling after a few months.