The time of the examination on the day of the veset

At what point during the days of separation (yemei perisha) should the examination be done?

Shalom u’vracha,

For a fixed cycle (veses kavua) – she must check twice during the onat ha-veset (anticipated time).

For an irregular cycle (veses she’eino kavua), - it is sufficient to perform one check at the end of the onah. 

For the average cycle (onah beinonit) – she should check twice during the anticipated time, because the onah beinonit is treated with the same stringency as a fixed cycle.

Collection of Laws of Purity by our teacher, the Gaon, Rabbi Ovadia Fried, shlita