Usually throughout a day. Not all babies often survive. Depends on breeding practices, how healthy the mother is, etc.

I've also found that molly and platy babies are visible the first couple of days, and then they seem to go into hiding before they eventually emerge a couple of weeks later. Depends on tank set up, I guess.

I would think that either she or some other fish ate the poor little guys! I had a couple of marble mollies at one time and the fathers would be eating the babies as she had them! no sooner did they come out did the father gooble it up! some little ones always survived but most were eaten.

I usually only notice one to three at first. They are so small and quick. Then, like Skygee said, in a week or two the population doubles to triples as they grow larger and brave out of hiding.