Guppy females usually drop their fry at the same time, though a GL observer felt that their female dropped fry at various times. Platys may drop a few fry everyday for a week or so. Colors, unless you have fry of the blue platy, should be different enough to tell them apart even when they are very young.

Except for mollies, I don't know of other popular livebearers or other mid-water swimmers in tropical fish tanks who are as tolerant of fry. Most residents of community tanks will snarf fry down right away.