Sexual Development of Mollies

Question
I have started up a main community tank. In it I have Mollies, platys, Angels and Loach.
I, like others, became excited at the site of a swollen belly, and disappointed to find my fish had lost their appetites one evening and the Belly was empty.
So I purchased one of these integrated (40L) tanks, and started watching for any fatso's, and in no time have dozens of fry in my nursery tank.
So here is the question.  Over the months I have seen fry develop into fully developed fish. The problem is that they ALL look the same basic sex.  
I would like to know how Mollies develop. Do they all look the same for  "X" months and then the male develops their distinctive characteristics. eg. Sailfin in the male salifin Molly.

Example,  I had a small Black-Molly. She was molested by a big platinum Molly. Before birthing, she was removed.  She died soon after birth, but the fry developed well to become what look like 1/2 size Platinum Mollies. Now I have no idea if they will continue to grow to full size Mollies, but I live in hope that I have created a miniature Platinum Sailfin Molly.
Again, my dilemma is that I really want there to be males and females, and yet they all look female.  So here again is that question, do fry all develop looking alike, until some age where the Sail unfolds and the Gonopodium magically appears in males?


Answer
From what I have researched the difference between male and female mollies is the dorsal fin and anal fin. However, I could not find any information as to when the fish develop. I have never bred mollies so I honestly do not know. If you cannot find answers you might have to do an experiment on your own. Once a new litter is birthed, examine them as best you can and try and see if you can tell the different between the male and females. If not than a week or so later examine them again and see if you can tell, continue until you can and when you can tell than that would be when they mature. However, I imagine it could be possible they are male and female at birth, they just may need to get big enough for you to tell. I probably have not been much help but I would advise asking one or more of the other experts, as one of them may have bred mollies or know more about the maturity of them. Sorry I couldn't help more. If you do find out about the maturity time, it would be great if you would let me know. I am always reading and gathering information, as there is tons for fish keeping, and I would appreciate learning anything more I can.
                                                Rachel A.