Back in the day, Michigan State went for two weeks or longer. We were still on quarters and school didn't start until late September. Between home football games and the Jewish holidays... Sometimes it was really a long, drawn out process. One year was especially bad. I think rush went for a full three weeks. It was awful for everyone involved.
I see MSU does it in eight days now. Of course, there are less chapters and fewer rushees so it's possible. There's no way we could have done it in eight days back then.