It's the same with any food. You feed what your shrimp can eat before the food has a chance to foul the water. For most foods, that's a couple hours. For Repashy, most leave the food in for 24 hours or more with no issue at all, as it's tank stable.
What is the "ideal" amount to feed, in a shrimp only tank? Enough to be eaten in 1 hour? 4 hours? etc?