Egg yolk: hard boiled - longer boiled, better
Take the yolk only, you can eat the white stuff.
Take a tiny pinch of yolk and ;
a. squeeze it around the water surface
b. dilute it in a cup of water and carefully pour evenly in the tank.
c. dilute it in a small spray and spray evenly on the surface.
If the water gets cloudy, you're using too much.
You can feed them as soon as they're free swimming - though half aren't free swimming yet. You can prepare bbs hatchery now or wait another 2 days to feed on the following day.
Good luck on your fry