Why are you going to remove the moms? If anything just remove the babies once you find them and put them in a breeder box. Usually you can not tell when a fish is about to labor (at least the livebarers).
Magafish the info of livebearers giving birth at dawn is wrong. I keep guppies and swordtails and many times i have watched them give birth during the day, usually the afternoon. It is very difficult to tell when individual females are going to birth unless you know their birthing history as some will be fatter than others at birth. Also females that are storing alot of unfertilised eggs can be fat but not be about to drop. My advice is to watch the gravid spot. Livebearers give birth every 28 days approx and when they are about to drop look at their anal passage where the poo/fry come out. When they are about to give birth it becomes more angular/squared to the body instead of rounded. For future reference when she does have her babies record the date and you will be better prepared if necessary the next time she births.
If your tank is densely planted then some of the fry should survive it really depends upon the other fish and how voracious they are.
In the tank where i have my angel i have never had a fry survive to catch despite it being heavily planted they are voracious and can smell a female birthing. . :mad2: