They didn’t ban release. They waited for all the mail-in ballots to arrive, particularly overseas and military. Friday was a holiday.
This is a new one on me. In every election, there are absentee and mail in ballots which are counted after election day. But the fact that those ballots may not have arrived by election day does not prevent the release of the election returns from election day itself.
Absentee ballots are not likely to change election results—or so it was, 25 years ago.
Court challenges and lawsuits were the reason. “U.S. District Judge William Conley rejected a request by Democrats and liberal groups to postpone Wisconsin’s election, but ordered that voters have until Monday (today)— six days after the election — to file absentee ballots. And Conley prohibited clerks from starting counts until 4 p.m. today.”
https://wkow.com/2020/04/13/clerks-set-to-count-votes-in-messy-wisconsin-election/