Why do some eggs last longer than others?

In ovulation an egg lasts 12-48 hours, anyone know why some last longer than others?

Is the egg not as good of a quality if it doesn’t last as long?

If your egg is waiting around for a long time and then gets fertilised could this be worse?

Do you technically stop ovulating once the sperm meets an egg? Causing a drop again so your tests would go back down sooner?

Why do I sometimes get two smiley faces (one day and the following day) and some months only one?