Election is 11/3. Most of the results are in by 11/4. Looks like Biden will win. States that are currently Republican controlled, but vote blue, decide to appoint new Electors to the College. They can do this by the end of the day. I expect they've already got the paperwork done.
Dems in the house could wait as long as possible and object to every single state as they read out their votes on 12/14. Republicans can be standing by to immediately receive the objection, say "No" and send it back. Longest I can see this lasting is the end of that week, 12/18.
All this time Trump is still president. How do you see Dems stretching this process for another 4 1/2 weeks? When does Pelosi become President?