One needs to start with the mechanics of the election process. The votes for members of the House and Senate can go on until the laws of the particular state say they must stop. That will settle the House and Senate races, though those can go on till past January 3, as happened with the Norm Coleman-Al Franken race in Minnesota.

The Presidential race is different. The electors vote on December 14, 2020, this year. Meaning, whoever is ahead in the state counting, that is when the electors have to cast their votes, based on the Constitution. It does not mean those votes need to be accepted by the House. But that is the initial count and election. The House is then free to disregard the electors of any state, if they can reach a majority of the states to do so, though it might be a majority of the House, not sure on that point. Baseline, the first presidential election ends on December 14,2020, the real one somewhere around 3 January, 2021 or a few days later, depending on process.