I've tried to raise fry that small (sexy shrimps) but can't get them past 10 or 14 days, due to feeding and water quality problems in the rearing tank.
Currently my molly miller blenny's are laying eggs continuously in my reef system, but separating them into a different tank without a reliable food source and effective filtering wouldn't work.
If I wanted to really try to get my a few of my blenny fry to settle out, I would have to remove all predators (including all stinging corals and other fish) and feed live phytoplankton, making the water green, which would feed the food chain upwards and hopefully provide enough larger zooplankton to get the fry large enough to consume baby brine shrimp. Not really worth the effort, but not impossible. I've read people posting about random survival of fry in their tanks.
The only success I've had are with cardinals, which are the easiest to raise since they come out big enough to eat baby brine. Even this was a major chore as I had to raise 2 batches of brine shrimp a day, one for the morning feeding and the other for the evening. Each batch was started 12 hours apart and also needed to be enriched for a day, so if I recall, I had 4 2L bottles of bubbling water going constantly for 2 months, until I got them onto dried food.