I have a phone call in to my Michigan DNR contact -- but haven't heard back. What I "think" it is -- walleye season does not open until Thursday morning 15th. So any pre-fishing prior to Thursday morning would have to be in Wisconsin waters.
I'll post back when I get the official word. Just didn't want you to think I wasn't planning to respond.
Walleye Season opens May 3rd from 45 degrees 15 minutes and south/east. That is the area known as Rochereau Point. However, north of that line does not open until the clock turns over to May 15th (just after Midnight). So you would have your pre-fishing on Thursday and Friday for north of that point. But your pre-fishing prior to Thursday needs to be confined to Rochereau Point (45 degrees 15 minutes) and sounth.