I would guess you look at total registration and start with 2016’s 75% turnout. That would be a reasonable first estimate.
FL registered 14.065M. 75% would be 10.5M. So the elections official is looking for 79%. VBM is generally accepted as increasing overall turnout and thus, 4% over 2016. Reasonable.
We’re going to walk into ED down 3-4% of remaining votes. About 2.5M out of 11. So it would be like seeing down 3.5% with 78% if the vote already in.
Reps do much better on election day, but the lower the burden, the better. Meaning hold them down tomorrow and Monday and for sure have more than 2.5M votes come in Tuesday.
Unless all the early voting just devastated election day turnout. (Hope not!)