Actually, I was reading up on them and the larvae can live in freshwater for up to an approx. 8 days. Within this time, you need to move them into water with around 30 ppm of salinity. Some suggest 17, but the article for breeding them said 30 ppm has a higher success rate.
What you can do is transfer the pregnant amano into a small 1 gallon tank, a few days before expected release. Once she releases all the eggs (which I believe takes 1-2 days), you remove the adult and put her back into the main tank. Then, you can change the 1 gallon tank into a brackish water tank for the larvae to grow. They can take on full force brackish water instantly, without having to be acclimated. Then you need to feed them green water and other microscopic foods. It takes about 40-60 days before they begin turning into mini shrimp. And you need to wait about another 20-30 days before you can slowly begin changing their water to freshwater with each water change.
You can google "Amano shrimp breeding" to find out more
