I released my molly fry (about a half-inch long, but stocky) after 4 weeks into the big tank. At that point, they are small enough to occasionally be chased, but too big to be eaten.
Now that they're in the big tank, it's been about 3 weeks and they're going strong. I don't feed them separately (it would be impossible); they find enough stuff on their own. I always see them picking at the decor, the glass beads, the sand, the
driftwood, etc. I have no algae, so I have no idea what they're eating, but they are growing. Sometimes I see them nip at a piece of fish flake that floats past the feeding frenzy of adults, but that's all.
OH. I do have the intake filter stuffed with filter fiber. Otherwise, they can get sucked to it and die.