The gemara (Shabbos 86a) says that the Torah was given either on the 6th or 7th day of Sivan.

Furthermore, the Torah was given on Har Sinai, but we don’t know where that is. 

“So we don’t know when the Torah was given and we don’t know where the Torah was given. This is to teach us that any time and any place is ideal for Torah.”

~ R’ Yisrael Salanter zt’l (1809-1883)