Rashi informs us that Moshe gathered the Jewish people the day after Yom Kippur. How does Rashi know that? Since the verse says that he gathered them meaning they were not together as a group. If the events of this week's portion occurred on the day that Moshe descended the mountain the Jewish people were waiting for him there and there was no need to gather them. The very fact that he needed to gather them means that it did not occur on Yom Kippur. And the next opportunity was the very next day