Hey llr89, congrats!! I'm not sure how many days they interview.
I spoke to an advisor at OU at the end of last winter, and she said last year they received about 150 applications, interviewed about 70, and enroll 40-44. Of course, they probably accept more than that number since some people accepted will attend another school too. So in other words, the odds seem to be pretty good once you reach this point! Of course, the number of applications received and people interviewed would vary from year to year too. Did you go to OU for your undergrad by any chance?
I'd be curious to hear from anyone who has gone through one of OU's interviews before to explain how the day went.