Is it correct or incorrect to delay ghusl to ensure the discharge of the white qassah when in doubt about the end of menstruation?

A woman recognizes purity from menstruation by one of two signs: dryness (the purity of the private parts after inserting a piece of cloth), or the white discharge (a white fluid). Whichever of these she sees first, she must perform ghusl immediately.

Some scholars have permitted waiting a day or half a day after seeing dryness during the customary period. However, if she sees the white discharge, she must perform ghusl immediately. If a woman doubts whether purity has occurred, the default assumption is that menstruation continues.