The U.S. Army War College has revoked the 2007 Master of Strategic Studies degree of Senator John Walsh (Democrat, Montana) because he plagiarized a research paper required to graduate. Walsh was the Adjutant General of the state National Guard before being appointed to fill Max Baucus' term.
Do you mean between the time he received his degree (2007) and now, or between the time they found out (late July 2014) and now? The Army War College (USAWC) apparently found out when everyone else did, from the New York Times this past July. Within 2 days of the article being published, USAWC referred the issue to their academic review board. The board formally started their investigation in mid August. Less than two months later, he was stripped of his degree. That seems to be reasonably quick. It is just enough time to do their own thorough investigation (rather that solely relying on the NYT), decide on the appropriate punishment, and implement it. Degree revocation is (IMHO) the most serious thing an university can do, to students or alumni. I consider it far worse than expelling a student. If you are wondering why it took 7 years to come out, my bet is that back in 2007 USAWC was not using extensive plagiarism detection tools, or perhaps the tools that they were using did not have the articles he plagiarized in their database. Who knows?