I'm legitimately terrified about what is going to happen. IF (all caps for a reason) Biden wins, it will not matter by how much. Trump will be declaring victory before dinner, in my opinion.
I think we're going to know early on election night.
A month or two ago a lot of liberals were publicly expressing fear that Democrats would be using mail in ballots while Republicans would vote on election day at the polls. The fear expressed by these people is that the "early returns" (i.e., election night totals) would favor Republicans and thus Trump and others would claim victory, then once all ballots are counted, claim their victory was stolen from them.
I actually think the opposite will happen. I think that people are going to vote early, in many cases in person, and those votes will be long tabulated before election day. Once the election day ballots are in, we'll pretty much have all the ballots counted, with a few stray mail in ballots to come in.
If the supposition is right (that early ballots or mail in ballots favor Democrats), something I don't necessarily subscribe to, Biden should see a very early lead, with a possible narrowing of the gap as the evening and following day wears on.