In Wisconsin, "early voting" is simply casting an absentee ballot in person at the clerk's office rather than by mail. The forms are all the same. The only differences are that you don't need a reason (though you never need a reason for voting absentee in Wisconsin), the clerk signs the envelope as your witness instead of some random person, and then you just hand it over instead of mailing it in.
Additionally, the bit about absentee/early votes not being counted until after the election isn't always true, and it's definitely not true in Wisconsin. Check out the
National Conference of State Legislatures' page on early/absentee voting for a state-by-state breakdown.