How late was Moshe?

The Abarbanel says, contra the midrash and Rashi, that there was no expectation of 40 days on the mountain.

I saw this in a rather nice sefer, Ateres HaMikra. The author quotes the pasuk and presents a short question, and then summarizes one or two answer from classic meforshim to this question.

Consider the pasuk and Rashi pasuk in Ki Tisa (32:1):

1. When the people saw that Moses was late in coming down from the mountain, the people gathered against Aaron, and they said to him: "Come on! Make us gods that will go before us, because this man Moses, who brought us up from the land of Egypt we don't know what has become of him."

א. וַיַּרְא הָעָם כִּי בשֵׁשׁ משֶׁה לָרֶדֶת מִן הָהָר וַיִּקָּהֵל הָעָם עַל אַהֲרֹן וַיֹּאמְרוּ אֵלָיו קוּם | עֲשֵׂה לָנוּ אֱלֹהִים אֲשֶׁר יֵלְכוּ לְפָנֵינוּ כִּי זֶה | משֶׁה הָאִישׁ אֲשֶׁר הֶעֱלָנוּ מֵאֶרֶץ מִצְרַיִם לֹא יָדַעְנוּ מֶה הָיָה לוֹ:

that Moses was late: Heb. בשֵׁשׁ, as the Targum [Onkelos] renders אוֹחַר, an expression for lateness. Likewise, [in the verse] “is his chariot late (בֹּשֵׁשׁ) ” (Jud. 5:28); “and they waited until it was late (בּוֹשׁ) ” (Jud. 3:25). When Moses went up the mountain, he said to them [the Israelites], “At the end of forty days I will come, within six hours” [from sunrise of the fortieth day]. They thought that the day he went up was included in the number [of the forty days], but [in fact] he had said to them, “forty days,” [meaning] complete [days], including the night. But the day of his ascent did not have its night included with it [because Moses ascended in the morning], for on the seventh of Sivan he ascended. Thus, the fortieth day [of Moses’ absence] was the seventeenth of Tammuz. On the sixteenth [of Tammuz], Satan came and brought confusion into the world and showed a semblance of darkness, [even] pitch darkness, and confusion, [as if] indicating [that] Moses had surely died and therefore, confusion had come upon the world. He [Satan] said to them, “Moses has died, for six [additional] hours have already passed, and he has not come, etc.,” as is found in tractate Shabbath (89a). We cannot say that their [the Israelites’] only error was that on a cloudy day [they were confused] between before noon and after noon, because Moses did not descend until the next day, as it is said: “On the next day, they arose early, offered up burnt offerings…” (verse 6).

כי בשש משה: כתרגומו, לשון איחור, וכן בשש רכבו, (שופטים ה כח), ויחילו עד בוש (שם ג כה) כי כשעלה משה להר אמר להם לסוף ארבעים יום אני בא בתוך שש שעות. כסבורים הם, שאותו יום שעלה מן המנין הוא, והוא אמר להם שלימים, ארבעים יום ולילו עמו, ויום עלייתו אין לילו עמו, שהרי בשבעה בסיון עלה, נמצא יום ארבעים בשבעה עשר בתמוז. בששה עשר בא השטן וערבב את העולם והראה דמות חשך ואפילה וערבוביא לומר ודאי מת משה, לכך בא ערבוביא לעולם. אמר להם מת משה, שכבר באו שש שעות ולא בא וכו', כדאיתא במסכת שבת (דף פט). ואי אפשר לומר שלא טעו אלא ביום המעונן בין קודם חצות בין לאחר חצות, שהרי לא ירד משה עד יום המחרת, שנאמר וישכימו ממחרת ויעלו עולות:

the following Q and A:

 ק. וכי בשביל יום אחד לפי דעתם שמשה איחר לרדת מן ההר ,מיהרו לבקש תחליף?ב

ת. (אברבנאל) משה רבינו לא אמר להם כי ירד בסוף ארבעים יום, ואולי גם לו לא היה ידוע מקודם כמה זמן יהיה בהר.  והם נקהלו על אהרן במשך הרבה ימים ואמרו לו יום יום  ׳קום עשה לנו אלהים שילכו לפנינו כי זה משה האיש לא   ידענו מה היה לו׳.

Q: Now because of a single day, according to their opinion, that Moshe delayed descending, they hurried to request a substitute?

A: (Abarbanel) Moshe Rabbeinu did not tell them that he would descend at the end of 40 days, and perhaps he himself did not know initially how long he would be on the mountain. And they gathered to Aharon at the end of many days and said to him, each day, 'arise, fashion for us gods that will go before us, for this man Moshe, we know not what has happened to him'.

End quote.

Perhaps we could further say that even this 40 was not in the original plan, as we see that Moshe only descends because the people have sinned. Perhaps he would have otherwise stayed up longer.

7. And the Lord said to Moses: "Go, descend, for your people that you have brought up from the land of Egypt have acted corruptly.

ז. וַיְדַבֵּר ה אֶל משֶׁה לֶךְ רֵד כִּי שִׁחֵת עַמְּךָ אֲשֶׁר הֶעֱלֵיתָ מֵאֶרֶץ מִצְרָיִם: