So they just hatched last night. Then you don't need to feed them just yet. The first few days after they hatch, they feed off the egg sack they came with. Of course the time vary by depends on the temperature and species. Generally speaking as long as you see the big round stomech on them, they don't need any outside food yet. However you might want to start giving some food when the stomech is shrink and almost roundness is gone.
Usually some small live food is better. Like microworms(walterworms), vinegar eels, BBS or some green water. You can also could transfer to the container some Moss like plants if you have them in the established tank. They have some micro organism the frys could eat. Also you could squeeze some dirty looking water from some established filter material like sponge or filter floss from the established tank. There are some microorganism the fry could eat. Just few drops would do.
You could buy some baby liquor food from the store. But you really have to watch not to foul water(no overfeeding!). I imagine the livebearer trap is attached to the parents tank. And have same water parameter? If so, you can change some water in the container daily. Especially little after you fed them using the water from the parents' tank that they have same water parameter.
You could also feed some yolk from the hard boiled eggs for emergency as I heard main ingridient of liquor fry is that. But I can never stress enough that you better make sure you don't overfeed. Since the frys are really sensible to the water quality. Also you could put gentle water movement by adding the airstone. And you could also set up bigger container 1~5G(depends on the number of frys you have) with sponge filter once they start free swimming and you start feeding.
Sponge filter is ideal but you can do with air stone and some daily water change if you do not have established sponge filter. You cannot use most other filter that the frys are too small and the most filter is either create too strong water movement or denger of sucking frys.
Anyway, good luck raising them. Also you could always research and read about how to raise Cory frys. I think there is a guideline in the main part of this site.
