Well, the fish probably won't care much, but they will get used to being fed at a specific time, and you can use this to train the shy or nocturnal fish to come out specifically for feeding. In the wild, fish feed throughout the day, with heavier feedings based on the activity of their foods--ie, mosquitos aren't active at high noon, so fish that feed on mosquitos aren't feeding at high noon either. In the aquarium, it's usually easier to provide a few meals, rather than a buffet line. I try to feed about the same time most days, but I don't freak if I'm a bit off.