EDIT: Wow we have very different timings. Could it be that the official site is so off the mark?
The times Dr. Maserati gives seems a tad more logical too (because there's the podium and all to be done after that).
Do they come from L'Equipe? If so, I would trust they are fresher and more up to date.
The official TdF website has tentative timings for the stage depending on the speed.
The riders shall enter Paris a little tad before 16h00 (4pm), coming from Charenton. They will then ride alongside the Seine river. They should enter the Champs Elysées circuit at 16h10 or 16h30. Stage should finish an hour after that.
My (incorrect?) source: