Bnei Yisrael had to prepare themselves for three days before the giving of the Torah.
As a parallel to this receiving of the Torah, the Jews "accepted" the Torah on Purim (kiy'mu v'kiblu). The turning point in the story occurs after Esther and her servants (and all the people) take 3 days to prepare themselves for her meeting with the king.
Are there commentaries which tie the specific events in the timeline of Purim to the timeline of Matan Torah at Har Sinai?