ANSWER:

This is something that was not mentioned in the Quran and sunnah.

Some scholars and schools of thought said that a woman must perform ghusul as soon as she sees her purity even for moments. This is too hard for women as it requires a woman to check on herself every five minutes and once she is dry she performs ghusul.  The problem is that she can easily see the blood coming back after having ghusul which means she was wrong in deterring her purity,. So, she checks after another 5 minutes and so on!

Other scholars say that if she saw this dryness after her usual time of period, she can perform ghusul as she is usually getting it for 7 days and these days are over. 

But if she saw it before that, Ibn Othaimeen and others say that she waits for 6 to 12 hours. 

On your website, you state that a woman should remain dry for at least 12 hours in order to make ghusl (take a ritual bath) after her period is over. My question is why can’t she just take a bath after 3-4 hours of being dryness… 12 hours is too long.. can you specify more on this subject… Where is the daleel about that.. what does the Qur’an say about it? Who determined the 12 hours?