I am also an international student, who focus on CMT. I was informed that I am on the waitlist of UMN since 2/17.
But until now, I check the mailbox and their website every day, no final decision is made.
I know some of the students who applied UMN Ph.D. have got the offer already ( and most of them will reject it because of the cold weather
). So if you don't want to go, it would be nice to reject it as soon as possible. UMN is my dream school.