when was naaseh v'nishna said?

According to Rashi, the events described in ch 24 of our parsha took place before mattan Torah: פרשה זו קודם עשרת הדברות.  The inevitable conclusion one must draw is, as Gur Aryeh writes, ויהיו לפי זה הפרשיות שלא כסדר.  The Torah here hits the rewind button and brings us chronologically back to the middle of parshas Yisro.  As Rashi reads the events of the perek, on 4 Sivan Moshe gave Bn"Y the mitzvos of perisha and hagbala and told them to prepare for mattan Torah, and Bn"Y responded (24:3) כׇּל־הַדְּבָרִ֛ים אֲשֶׁר־דִּבֶּ֥ר ה׳ נַעֲשֶֽׂה׃.  Next day Moshe wrote out the parshiyos of Torah.  On 6 Sivan he read what he had written to Bn"Y, and this time around Bn"Y responded with the famous line that we all know  וַיֹּ֣אמְר֔וּ כֹּ֛ל אֲשֶׁר־דִּבֶּ֥רה׳ נַעֲשֶׂ֥ה וְנִשְׁמָֽע׃ (24:7)   

Ramban on the spot disagrees and writes that these events took place only after mattan Torah.  There are two things to be gained by taking this approach.  1) The order of the text does not deviate from the chronological order of events -- we don't have to rewind to anywhere.  2) The answer to Tos question of why Hashem had to hold Mt Sinai over the people and threaten to crush them if they did not accept the Torah when the people had already declared נַעֲשֶׂ֥ה וְנִשְׁמָֽע is simple -- נַעֲשֶׂ֥ה וְנִשְׁמָֽע was said only after kabbalas haTorah, not beforehand.  

That being said, the glaring issue with Ramban, which he raises himself at the very end of his comment, is that Chazal present נַעֲשֶׂ֥ה וְנִשְׁמָֽע as a great statement of faith on the part of Bn"Y in that the people accepted Torah sight unseen, details unknown.  This has so seeped into our consciousness as part of our mesorah that to disregard it seems almost impossible.  How then do you square the pshat reading advanced by Ramban that  נַעֲשֶׂ֥ה וְנִשְׁמָֽע was said only after mattan Torah with this mesorah?  I don't have a good answer and I don't understand how Ramban squares the issue away.   

Turning back to Rashi's reading, there were two responses by Bn"Y before mattan Torah.  On 4 Sivan the response was only נַעֲשֶֽׂה; two days later the response was נַעֲשֶׂ֥ה וְנִשְׁמָֽע.  Why the change?  Why didn't Bn"Y respond with נַעֲשֶׂ֥ה וְנִשְׁמָֽע the first time around?  What changed?

Shem m'Shmuel answers that there has to first be a kabbalah of plain vanilla נַעֲשֶֽׂה, even without understanding, no questions asked.  Once a person is prepared to accept things on that level, then they are capable of נַעֲשֶׂ֥ה וְנִשְׁמָֽע, of aspiring to understand.  

(Chasam Sofer has a chiddush gadol on the gemara's statement (Shabbos 88):

 רבי אלעזר בשעה שהקדימו ישראל נעשה לנשמע יצתה בת קול ואמרה להן מי גילה לבני רז זה שמלאכי השרת משתמשין בו דכתיב ברכו ה' מלאכיו גבורי כח עושי דברו לשמוע בקול דברו ברישא עושי והדר לשמוע. 

He writes that davka malachim need נַעֲשֶֽׂה to be able to come to נִשְׁמָֽע.  Bn"Y, however, are banim laMakom.  For us, we don't need any preparation or precondition, not like the Sm"S.  The gemara means the opposite of how we usually read it.  It is not complimenting us that we achieved what only angels could achieve.  Aderaba, מי גילה לבני, why are those who are  בני behaving in a way that is appropriate for angels, who are on a lower level!)

Perhaps one can say that on 4 Sivan there was not yet a text of Torah, and therefore, there could be no aspiration for נִשְׁמָֽע.  The thought that a human being can understand G-d or connect with G-d is on its face almost sacrilegious.  How can you dream that your mind can comprehend even one iota of dvar Hashem?  It's only by virture of Torah that we have a means to do so, as the Baal HaTanya explains in ch 4:

וְאַף דְּהַקָּדוֹשׁ־בָּרוּךְ־הוּא נִקְרָא "אֵין סוֹף", וְלִגְדוּלָּתוֹ אֵין חֵקֶר, וְלֵית מַחֲשָׁבָה תְּפִיסָא בֵיהּ כְּלָל,

וְכֵן בִּרְצוֹנוֹ וְחָכְמָתוֹ,

כְּדִכְתִיב: "אֵין חֵקֶר לִתְבוּנָתוֹ",

וּכְתִיב: "הַחֵקֶר אֱלוֹהַּ תִּמְצָא", וּכְתִיב: "כִּי לֹא מַחְשְׁבוֹתַי מַחְשְׁבוֹתֵיכֶם".

הִנֵּה עַל זֶה אָמְרוּ: "בְּמָקוֹם שֶׁאַתָּה מוֹצֵא גְּדוּלָּתוֹ שֶׁל הַקָּדוֹשׁ־בָּרוּךְ־הוּא, שָׁם אַתָּה מוֹצֵא עַנְוְתָנוּתוֹ",

וְצִמְצֵם הַקָּדוֹשׁ־בָּרוּךְ־הוּא רְצוֹנוֹ וְחָכְמָתוֹ בְּתַרְיַ"ג מִצְוֹת הַתּוֹרָה וּבְהִלְכוֹתֵיהֶן,

וּבְצֵרוּפֵי אוֹתִיּוֹת תּוֹרָה־נְבִיאִים־כְּתוּבִים,

וּדְרָשׁוֹתֵיהֶן שֶׁבְּאַגָּדוֹת וּמִדְרְשֵׁי חֲכָמֵינוּ־זִכְרוֹנָם־לִבְרָכָה.

בִּכְדֵי שֶׁכָּל הַנְּשָׁמָה אוֹ רוּחַ וָנֶפֶשׁ שֶׁבְּגוּף הָאָדָם, תּוּכַל לְהַשִּׂיגָן בְּדַעְתָּהּ,

וּלְקַיְּימָן – כָּל מַה שֶּׁאֶפְשָׁר לְקַיֵּים מֵהֶן בְּמַעֲשֶׂה דִּבּוּר וּמַחֲשָׁבָה,

After Moshe had written down a text and there existed a cheftza shel Torah which Hashem's chochma was miraculously connected to, we then had the means to think about נִשְׁמָֽע.