For starters, it would almost certainly occur after Trump leaves office on January 20, when Democrats take control of the Senate, according to the Washington Post. McConnell's memo notes that the Senate will not reconvene until January 19 for any substantive business - leaving the day before Joe Biden's inauguration as the earliest possible date for proceedings to begin.
Although the Senate will hold two pro forma sessions next week, on Jan. 12 and Jan. 15, it is barred from conducting any kind of business during those days — including "beginning to act on received articles of impeachment from the House" — without agreement from all 100 senators. With a cadre of Trump-allied senators in the Republican conference, that unanimous consent is highly unlikely. -Washington Post