This section from the Haggadah:
Pesach Haggadah, Magid, Story of the Five Rabbis 1:
מַעֲשֶׂה בְּרַבִּי אֱלִיעֶזֶר וְרַבִּי יְהוֹשֻׁעַ וְרַבִּי אֶלְעָזָר בֶּן-עֲזַרְיָה וְרַבִּי עֲקִיבָא וְרַבִּי טַרְפוֹן שֶׁהָיוּ מְסֻבִּין
בִּבְנֵי-בְרַק וְהָיוּ מְסַפְּרִים בִּיצִיאַת מִצְרַיִם כָּל-אוֹתוֹ הַלַּיְלָה, עַד שֶׁבָּאוּ תַלְמִידֵיהֶם וְאָמְרוּ לָהֶם רַבּוֹתֵינוּ הִגִּיעַ זְמַן קְרִיאַת שְׁמַע שֶׁל שַׁחֲרִית.
It happened once [on Pesach] that Rabbi Eliezer, Rabbi Yehoshua, Rabbi Elazar ben Azariah, Rabbi Akiva and Rabbi Tarfon were reclining in Bnei Brak and were telling the story of the exodus from Egypt that whole night, until their students came and said to them, "The time of [reciting] the morning Shema has arrived."
I don't recall offhand which page(s) in Masechet Brachot discuss(es) the earliest time for reciting the morning Shema (someone, please edit). But, IIRC, there was a debate.
The beginning of the Hagadda says:
וְכָל הַמַּרְבֶּה לְסַפֵּר בִּיצִיאַת מִצְרַיִם הֲרֵי זֶה מְשֻׁבָּח.
And anyone who adds [and spends extra time] in telling the story of the exodus from Egypt, behold he is praiseworthy.
Perhaps, the students used the earlier ruling regarding the Shema; perhaps, their ruling may have differed from those of the rabbis; perhaps, the rabbis themselves differed in their practices; perhaps, even if they used the early time to begin Shema, there may have been an exception because they were learning.
The point is, if they could have used the later time instead of the earlier time, they would have fulfilled the mitzvah of spending more time discussing the Hagada, as suggested in the above paragraph.
So, Which ruling did the (students of) these rabbis follow?