Ideally its best to wait for the tank to cycle all the way through until you get no ammonia or nitrites when you measure your parameters. The visual cue is to wait for the white cloudiness of the water to go away, that means the good bacteria is breaking down everything to the nitrate form which is far less harmful to fish than ammonia or nitrates. But IMO feeders are there for two reasons, to feed bigger guys, and to cycle tanks. If it was me I'd just dump them in