The duty of prayer after menstruation cannot be settled merely by saying that some prayer time remains. The discussion concerns how much time is available for the relevant purification and the prayer, as well as when bleeding ceased.
Cessation at ten days and cessation before ten days are treated differently in determining obligations. The remaining prayer period and the possibility of purification must also be considered together.
This illustrates how a reading's meaning becomes a legal rule only when the other applicable conditions of worship are accounted for.