Is it necessary to perform ghusl after a drop of blood appears on an unspecified day after the menstrual period has ended, given that it is neither small nor large? And is Maghrib considered the start of the next day of the period, or is it Fajr Adhan?

All blood a woman sees during the first fifteen days is considered menses (hayd) and necessitates ghusl (ritual bath) after its cessation, even if the blood is scant or returns before the end of this period. As for what occurs after the fifteen days, it is considered irregular bleeding (istihadah).