The first day might start in the middle of the day, if she first saw her flow in the afternoon. But whenever they began, they end on the night after the fifth day, as we will discuss below. For example, if she first saw blood on Sunday, whether it was Sunday morning, or Sunday afternoon, or even Sunday evening ten minutes before sunset begins, Thursday is the fifth day. If she sees blood on a Saturday night, Sunday is still the first day of the five days, and therefore Thursday is still the last day of the five days. Remember, our days begin when night begins.
Gentile days go from midnight to midnight, but Jewish days go from nightfall to nightfall.
Once she has stopped seeing blood, she can begin the count of the Seven White Days. It means that she has completely stopped seeing blood. The Seven White Days begin when the woman, before sunset, takes a shower or bath, and cleans herself thoroughly, everywhere, or at the very least in that area. If it comes out clean, then the next day is the first day of the Seven White Days. The Seven White Days are not simply days of waiting.