To get to the ferry, put this address in your navigating system
215 WI-42, Ellison Bay, WI 54210. Do not be alarmed if it says the location is permanently closed. It is not. If there is a long line of cars on the right side of the curvy road, join the line. You can walk or drive to a little hut on the dock where you can buy your ferry tickets. If the line is long you could wait awhile, but generally not more than an hour.
The ferry does not take reservations. Through Thursday June 13th the ferry runs to Washington Island on the hour from 8 AM to 6 PM.
On June 14th the ferry starts its summer schedule and it leaves on the 15s and 45s of each hour until 6:45 PM. There are some later trips on Friday nights only (see https://wisferry.com/washington-island/ for details). If you are in the ferry line 15 minutes before the last ferry, the ferry line will run extra boats to make sure you get to the Island.
Likely you will wait about 30 minutes for the ferry, but it is a very busy weekend on the Island so the line could be long and you could wait awhile.
Anywhere on the island will be 15 minutes or less (by car) to the wedding or pretty much to anywhere else on the Island.