This also includes having backup and maintenance for possible hitches etc.
Then it's the responsibility of the communities to have in place staff, facilities etc. ready for the project to expedite the ballots in a an equally timely manner. They are certainly instructed and briefed how this is to be done etc with plenty of time ahead of an election to be fully prepared for the count.
If you were going to set up a massive fraud operation, that would be a crucial component. In person votes would be much harder to manufacture in large numbers, so you count those first, which then closes the door on the in-person vote count, but leaves the number of outstanding mail-in ballots totally up to the imagination. Then they can claim any number of votes to be counted that they want to, limited only by their ability to fill in and submit those votes. At that point, the final tally is entirely at the mercy of how many mail-in ballots suddenly happen to just show up, even days after Election Day in a number of crucial states.
Just as with the dems visceral aversion to voter ID, you dont act this way unless youre trying to commit fraud.