For instance, it makes much more sense if Snow White grew up at the dwarves', so that there were gaps of years between the queen's attacks -- perhaps the mirror worked only so often -- which would give her time to forget and be sloppy.
But one tale motif really makes the time issue urgent. It involves a man who gets three pieces of advice on a journey. The last one cautions against being angry and violent too quickly. When he arrives home, he sees his wife with a handsome young man, but remembers the advice and gets her attention. Whereupon she calls her son to come see his father, who's returned home.
You go back and look at the tale, and you really can't figure out how on earth he managed to spend enough years that he left before knowing his wife was pregnant and returned after the son was old enough for him to suspect infidelity.