If your going to use the breeding box (which I use) you have to make sure you have a place to put the babies afterwards because being in that small a space can stunt their growth. I recommend their own separate tank until they are big enough or putting in lots of floating pants and hiding spots. When she looks like she is going to burst, her gravid spot is dark (which is not the most reliable way to tell because they differ for every fish), she doesn't eat and isn't very active, is hanging out in corners away form other fish and is being bothered by males then she's ready to go. Only out her in the box when you're sure it's time and never leave her in for more than 24hours. Don't move her in and out a lot because that'll stress her out too much. If she's seems like she is hurting her self or freaking out let her out. When you put her in either turn out the lights in the room or cover the tank up because they're more relaxed when it's dark.
This is all based on my personal experiences with my platies it may not work for everyone because my fish is very calm. I've had a pretty good success rate with this method but like I said it might not work for everyone. If it doesn't work in 4-6 weeks you'll be able to try a new method. I have pineapple platies in case you were interested.
