Nisaa
No. If bleeding that is hayd begins before the sun has fully set, that day's fast is broken and the day is made up later. Minutes make no difference. If the blood only appears after sunset, the fast is complete. This page covers the three versions of the situation: blood before Maghrib, a feeling that it is coming but nothing yet, and noticing blood after you have already broken your fast and not knowing when it started.
If the blood appeared before sunset
A fast runs to nightfall. Allah says: ﴿ثُمَّ أَتِمُّوا الصِّيَامَ إِلَى اللَّيْلِ﴾ "then complete the fast until the night" (Surat al-Baqarah 2:187). The Prophet (Salla Allahu 'Alayhi Wa Sallam) said: "When night comes from here, and the day goes from there, and the sun sets, then the fasting person has broken the fast" (narrated by al-Bukhari and Muslim, from 'Umar radi Allahu 'anhu). Hayd cancels the fast from the moment it begins. Abu Sa'id al-Khudri (radi Allahu 'anhu) narrated that the Prophet (Salla Allahu 'Alayhi Wa Sallam) said: "Is it not the case that when she menstruates she does not pray or fast?" They said, "Yes." (narrated by al-Bukhari and Muslim). So a period that begins at 5:50 with Maghrib at 6:00 breaks that day's fast, exactly as one that began at noon would.
The day must then be made up. 'A'ishah (radi Allahu 'anha) said: "We used to menstruate at the time of the Messenger of Allah (Salla Allahu 'Alayhi Wa Sallam), and we were commanded to make up the fasts, but we were not commanded to make up the prayers" (narrated by Muslim). Al-Nawawi (Shafi'i) in al-Majmu' and Ibn Qudamah (Hanbali) in al-Mughni both record that the scholars are agreed that a menstruating woman does not fast and must make up the missed Ramadan days, and IslamQA's ruling on the question reports no difference between the four schools on a period that begins just before sunset. This follows the same ruling as any other time of day; see what to do if your period starts mid-fast in Ramadan for the whole day, and how to count the fasts you owe for the make-up.
If you only feel it coming
Many women feel the cramps or the sensation of blood moving a little before it shows. Shaykh Ibn 'Uthaymeen (Hanbali) ruled that if a woman feels that menstrual blood is starting to flow but it does not actually emerge until after sunset, her fast is valid and she does not make up that day, because the ruling attaches to the blood's emergence, not the feeling (IslamQA, ruling 50282). That is one scholar's position, relied on by many, and the safest course is to check as soon as you can. If you are unsure, ask a scholar you trust, and see does brown discharge in Ramadan break your fast for how timing and the look of the discharge are judged on an ordinary fasting day.
If you only noticed after Maghrib, and don't know when it started
You break your fast, go to the toilet or change, and find blood. When did it begin? IslamQA's answer (366204), citing the principle that an event is attributed to its nearest time, says the following. If you think it most likely that it began before sunset, the fast is broken and made up. If you think it most likely that it began after, the fast stands. If you honestly cannot say either way, the fast is treated as valid, because the original position is that you completed the day until something is established to invalidate it. Sheikh al-Shanqiti is quoted there that, in genuine doubt, "the original ruling is that she fasted a complete day." The same reasoning applies to whether Maghrib prayer was valid.
What happens to the prayer of Maghrib
If hayd began before sunset, you do not pray Maghrib, because a woman in hayd does not pray (the hadith of Abu Sa'id above) and you owe no make-up for it. If the blood began after the time of Maghrib had begun, a different question arises, and the schools discuss it; see what to do if your period starts before you have prayed for that.
What to do on the day
Break the fast with the others if you are sure; there is no need to hold on to the last minutes. Note the exact time you first saw blood, since that is the thing every ruling above turns on. A tracker that records the time and the day helps; see the best period tracker for Muslim women for what to look for. Later, if your period ends mid-day rather than overnight, see period ends mid-day in Ramadan: do you fast.
This page is a study aid compiled from cited classical sources. It is not a fatwa. For your own situation, ask a scholar you trust.
