Kelliet,
It's great that your concerned about your fish, but...we do not need the forum clogged up with multiple threads about when your platies are due to give birth. You have already been directed to threads that give you all that information.
You do not need to do anything with your pregnant fish. You do not need 'hatcheries', or breeder boxes, nor do you need to know exactly when each female is due. All you need to provide is good food and plenty of clean fresh water in a sensibly sized tank, along with plenty of live plants for the fry to hide in.
Fish have been reproducing, perfectly happily, without human intervention for many thousands of years. The best thing you can do is leave them alone to get on with it. You will, if you provide the food, space and clean water, soon have more fry than you can cope with, believe me.