i find with all my livebearers, platys, swordtails, guppies, mollies, that a tell tale sign of when to put them in a breeding trap or tank, is when they suddenly look like there about to pop! and start floating near the bottom of the tank. and i also suggest you let the females rest in a different tank with either very placid fish or other females or by herself otherwise she will useualy die, as i have found out when i started in the hobby, the males seem particularly dependent on breeding straight after they having given birth.