I was wondering the same thing, I just had an interview there last week, during the interview they told me that I would hear back within 3 to 5 days, and then the day after I got an email saying it would take 2-3 weeks.
The email is a mass generated email. I got the same email and yet I heard the week after. If you got in, in most cases you'll hear back either the end of the week of the interview or the following week.
I interviewed on the 13th of this month and got my acceptance email on the 16th., even though they told me it would take 2-3 weeks. I don't know how it works for the oat, but I have yet to take one of the pre-reqs, which didn't affect or delay their decision making process. I would call them if I were you just to make sure.