Tosfot’s Opinion – Moshe Came Down on a Monday

Tosfot writes that the reason that Monday and Thursday were chosen as days to read the Torah is because these were days on which Moshe ascended and descended from Mount Sinai to receive the second set of tablets. He ascended on a Thursday, and he came back down with them on a Monday. Since the time when Moshe got the second tablets was a time of Divine goodwill, both of those days are considered days of Divine goodwill (עת רצון).

According to this opinion, the day that Moshe informed the people to stop bringing the donations was Friday, and he did so because Shabbat was approaching.