From 3:26 to 3:44 a.m. in the Associated Press election reporting stream, the vote for former Vice President Joe Biden jumped by 149,520 (9.2% of Biden's total votes) and Trump's vote jumped by 31,803 votes (2% of his total votes). Milwaukee County accounted for most but not all of that jump.

These votes were all reported together because Milwaukee and 38 other communities used a central count location. Other communities counted absentee ballots at the polling places, and reported them along with their in-person vote totals.

The city of Green Bay reported its results in bulk shortly after. It also had a central count facility for absentee ballots.

In other words, it’s not fraud, that’s just the time officials finished counting those legitimate votes.