In an extenuating circumstance, one can say the night time K'riyat Sh'ma until Netz, as per this statement:

If one didn’t say it then, make sure to complete it by Chatzot (midnight) and after the fact, one can still say it until Olot HaShachar. If one was in extenuating circumstances one may say it until HaNetz HaChama. (S”A 235:4-5, Mishna Brurah 235:27, 30)

I found in M"B 239:29

אבל בנאנס אפילו אחר שעלה השחר רק שהוא קודם הנץ נמי קורא ויוצא

The earliest time one may say Sh'ma in the morning is (under extenuating circumstances), is discussed here.

The earliest time for shema or Brachot shema is when one can recognize an acquaintance from 4 amot away called Mesheyakir, which is one hour (in Shaot Zmaniot) before HaNetz HaChama.

If the case could be established with such extreme circumstances that someone could only say Sh'ma before Netz, and he would not be able to say it later, and was not able to say it beforehand, could that one recitation count as both his night time and his morning saying of the Sh'ma?

I know that (according to the same Halachipedia site) Sh'ma said before bed can, in limited cases, count as both the Sh'ma al hamita and the evening Sh'ma so there is some (not strictly parallel) precedent for one recitation to fulfill 2 obligations.

No it cannot. In fact, one cannot even recite shema twice in the period between alot hashachar and hanetz hachamah to count for the evening and morning readings.

Shulchan Aruch Orach Chaim 58:5:

אם נאנס ולא קרא ק"ש ערבית עד שעלה עמוד השחר כיון שעדיין לא הנץ החמה קורא ק"ש ויוצא בה ידי חובת קריאת שמע ערבית ואם היה אנוס באותה שעה לצאת לדרך מקום גדודי חיה ולסטים לא יקרא אז ק"ש פעם שנית לצאת בה ידי חובת ק"ש של יום שמאחר שעשה לאותה שעה לילה אי אפשר לחזור ולעשותה יום:‏

If one was under duress [a circumstance that prevented one from reading Shema at the appropriate time], and didn't recite the evening recitation of the Shema until daybreak, since the sun has not yet budded, one may recite the recitation of the Shema and fulfill the obligation of the evening recitation of the Shema. And if one was under duress at that time - [for instance] to travel in a place with bands of wild animals and bandits - one should not recite the recitation of the Shema a second time to fulfill the obligation of the daytime recitation of the Shema because once one made that time "night," it's impossible to retract and make it "day."

(Translation courtesy of sefaria.org)

The Aruch Hashulchan in 58:8 quotes the Bet Yosef (Seif 8) that if you read Sh'ma after dawn to fulfill your nighttime obligation, you may not read it again until after sunrise to fulfill your daytime Sh'ma obligation; once you've declared this period as night you cannot redeclare it as day.

אם נאנס ולא קרא קריאת שמע ערבית עד שעלה עלות השחר, כיון שעדיין לא הנץ החמה – קורא קריאת שמע, ויוצא בה ידי חובת קריאת שמע של ערבית. ואם היה אנוס באותה שעה לצאת לדרך [במקום] גדודי חיה ולסטים – לא יקרא אז קריאת שמע פעם שנית לצאת בה ידי חובת קריאת שמע של יום, שמאחר שעשה לאותה שעה לילה – אי אפשר לחזור ולעשותה יום. ‏

This is learnt from Brachot 82b:

As it was taught in a baraita that Rabbi Shimon ben Yoḥai said in the name of Rabbi Akiva: At times, one recites Shema twice during the day, once just before sunrise and once just after sunrise, and he thereby fulfills his dual obligation to recite Shema: One, that he recites after sunrise, Shema of the day, and one, that he recites before sunrise, Shema of the night.

Since he doesn't suggest the more novel scenario of doing what you propose, the Bet Yosef proves that it cannot be done.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .