Watson, do they go on a "fast" while breeding? Mine seem to starve themselves once there are eggs in the tank. they literally will only eat a fraction of their normal portions.
I'd recommend when they're around 1 cm or so. Or you can just set up another tank and move the parents + Mimic the conditions, although moving the babies is easier for some to do.
If your wondering how I know this, we only have like a million Jag babies
Almost enough to use them as feeders