The main question here is:
Did they include into the prediction the fact that in many state mail in ballots have to be counted after normal ballots and that for a lot of reasons Democrats are way more likely to vote by mail.
EDIT: Not that it matters anymore by know.
My impression is that that is not the case as it was 4 years ago. Many of the swing states seemed to be committed to having all the results in within a few hours of polls closing, with some small exceptions. I believe that was the case in NC and GA, and with PA being expected to be closer to 4 hours after polls close.
It's definitely still a thing at least in some states.
And takes up to 3 days as it's more work then processing the normal ballot votes (especially if the normal votes are done with voting machines).
but is quite unlikely to change the outcome with how things look by now.