Following this question's comments, I wondered:
In what form did the Jews "receive/accept" the Oral Torah on Purim, was there some kind of a ceremony, or nation-wide event, maybe some other one-time miracles on the day of the original Purim, (that I'm unaware of) or was it gradual involvement in studying and discussing the oral law that resulted in emerging of the Sages as we now know them?
The Gemmorah in Bavli tells us (Shabbos 88a) they merely "started to observe":
אמר רבא אף על פי כן הדור קבלוה בימי אחשורוש
דכתיב קימו וקבלו היהודים קיימו מה שקיבלו כבר
Rava said: Even so, they again accepted it willingly in the time of Ahasuerus, as it is written: “The Jews ordained and took upon them, and upon their seed, and upon all such as joined themselves unto them” (Esther 9:27), and he taught: The Jews ordained what they had already taken upon themselves through coercion at Sinai.
Actually, Yerushalmi (Brochos 67b) also says that they simply agreed [on it]:
מגילת אסתר "קיימו וקבלו" וגו':
רב אמר וקבל כתיב, מלמד שהסכימו.