If MIN wants Wiggins, they will wait the 30 days. Without being signed, his salary wouldn't count for outgoing salary in a deal, so this actually makes a trade easier, since Cleveland needs to send out about $10.7 million in salary to acquire Love, and Wiggins can count for half of that.
As DOS said, it starts a clock for the other teams wanting Love. They have 30 days to convince Minny that their offer is better -- it doesn't really create much of an opportunity for the Celtics aside from as a 3rd or 4th party in any deal. Which is basically where we were before, but now we have a timeframe.