at the 78°-80°F temp range, most livebearers have their babies after about 28 days. dont put them in the breeder box until at most 24 hours before they are due to drop their babies. it stresses them out being in such a small space. if you are unsure of when they will have their babies, provide floating plants (real or fake) to give the fry places to hide, then suck them up with a turkey baster and put the fry in a breeder net or spare tank