Sounds great, the workingbikes warehouse will be open then too, so that might be a good place to go in and say "give me the cheapest working bike (no pun intended) that you have!"
I have no idea about the laws. Here's the thing: I'm guessing a lot of the good places to ride off (piers, docks) are privately owned. A lot of the open stuff is rocky. Of course, I don't know the whole lakefront. I'm sure that any kind of security wouldn't be too happy about it, illegal or not. So if you find an area thats decent without anyone around, it would probably go off without a hitch.