Is the temporal estimation of the menstrual period in the absence of seeing dryness correct, and what is required if the yellowish discharge does not cease, and is dryness for a few hours considered a sign of purity?

If the yellowish discharge occurs during the menstrual period and continues with blood for more than fifteen days, you are considered to be experiencing istihada (non-menstrual vaginal bleeding), and you should differentiate between menstrual blood and istihada. However, if the duration of the blood and yellowish discharge does not exceed fifteen days, then all of it is considered menstruation according to the Shafi'i school. But what we issue as a fatwa (definition), and which is more lenient, is that the yellowish discharge after seeing purity is not considered menstruation. So, whenever you see purity by dryness, perform ghusl (definition) (ritual bath) and pray, and do not pay attention to any yellowish or brownish discharge you see after that.