[stylin19a]

20th amendment solves that.(or is supposed to) A noon ending is also a noon beginning. I haven't chased down any US code.

"The terms of the President and Vice President shall end at noon on the 20th day of January, and the terms of Senators and Representatives at noon on the 3d day of January, of the years in which such terms would have ended if this article had not been ratified; and the terms of their successors shall then begin."

It seems the timing (the early taking) of the oath is a different question not solved by the Constitution.(Which the 20th amendment was supposed to solve) (Nor was the question asked by the MSM - go figure)

Article 2 Sec 1 Clause 8

"Before he enter on the Execution of his Office, he shall take the following Oath or Affirmation:—"I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my Ability, preserve, protect and defend the Constitution of the United States."

[Cletus.D.Yokel]

“Before he enter”.
If he /entered/ before noon on 20Jan2021 (just like Trump, 4 years ago) would not his “term of the President”...”end at noon” on the 20th day of January.

Hey, if the left wants to play HUmpty Dumpty, we can too.
And, I posit, we can because the Constitution has been suspended.