“There are no timing limitations on the use of the Impeachment process in the Constitution. So there is no limit in the Constitution for impeaching someone after they have left office.”
Please, that wasn’t my comment. That comment was in italics, which means that it’s somebody else’s. I then responded to it pretty much saying what you just said.
Parsing the constitution will not resolve the outcome. Plain words can be twisted to mean the opposite of what they say. Courts and Congress are professionals at this.