When's the best time to buy a pass - Today! There is no better time than today because its a rolling 12 month pass. Get one in November in Wisconsin and its only good for two months, same for Michigan. Minnesota treats you right with a full 12 month pass for only $25.
I've visited many Minnesota State Parks. But not as many as Anne Arthur author of Minnesota State Parks. Anne wrote the guide to Minnesota State Parks. The definitive companion guide gor your park adventures.