According to the timeline, when is the President of the United States really chosen?

Answer: The President of the United States is officially elected on January 6th when Congress counts the state electoral votes
Explanation: Since the mid-20th century, Congress has met in a Joint Session every four years on January 6 at 1:00 p.m. to tally votes in the Electoral College. The sitting Vice President presides over the meeting and opens the votes from each state in alphabetical order. He passes the votes to four tellers—two from the House and two from the Senate—who announce the results. House tellers include one Representative from each party and are appointed by the Speaker. At the end of the count, the Vice President then announces the name of the next President.