I just had platy babies, I can tell because the mother was thinner. There is a male that followed her around a lot, but I think it was for the food. She was a sunburst platy. I also have a pregnant dalmation platy, and two pregnant lyretail molly's. I have the same problem as you. I have saved 5 babies out of who knows how many and 3 of them are orange like the one I think is the mother. But then there are also the other two that are really dark brown. I have only had them for a few days so I cant really see any color changes. However, I am trying to figure out which are male and which are female. They are so small that I cant see. I see a bottom back fin but I cant tell if it is a 'female' fin or just the fin in front of either fin. Then again my males dont fan out their fins in front of the male reproductive fin. I guess what I am trying to say is that I imagine it would take atleast a couple of weeks. I was either told or read that I would have to keep them seperate for a month so they can grow big enough not to be parent food. Good Luck.