how long until we know the official results from the election?

Depends

1. Trump wins in a landslide and won't matter.

2. Trump mins by small margin.

3. Biden wins and it doesn't matter.

I'm sticking with #1

Depends on how close it is.

Long enough for the DNC to find several hundred thousand Biden votes in the trucks of cars in key swing states.

When you begin your day on 4 Nov 20, nobody will know who won. It will take days, if not weeks, to settle it. The Dems have every intention of waging Lawfare to contest every county that they can. The Dems have an army of election lawyers positioned and standing by to begin filings in any county or parish court in the USA.

The Dem strategy is to foment massive chaos and uncertainty. Blame Trump for the chaos and turmoil, because the polls and exit polls say he lost and Trump refuses to "do what's best for our Democracy." Then call on government and the courts to put an end to the chaos by ruling in favor of the "likely popular vote winner Joe Biden". The matter drags out long enough to become more and more of a crisis situation. Pressure applied by mass media propaganda builds on Trump by calling on him to concede. Pressure applied personally on the judges and Justices deciding election law cases in favor of Biden in order to "end the crisis created by Trump's refusal to concede."

Will it work? I don't know. But I am confident that the Dem plan is to use the Hegelian Dialectic approach to this situation: (in brief) Thesis - Antithesis - Synthesis. They will create chaos, blame Trump for the chaos and call on him to concede, utilize all propaganda and direct pressure means to persuade the people and the courts towards implementing the Dem solution - the Synthesis - of installing Biden as POTUS-elect - For the Good of Our Democracy.

We won't know the final results until Democrats can harvest enough ballots to win. shite may go well into January.

When ACB drags her, uh.. when ACB politely and demurely goes to bed the night before she has to publicly decide the winner and she giggles to her husband before going to sleep, and sweetly says, "Tomorrow, I'm going to make America great again! Goodnight, honey."

My expectation is that we will not know officially until after Thanksgiving. Every single state will be contested and fought in the courts by whomever loses that state, no matter what the margin is.