My understanding is as spots become available, the committee will meet periodically and discuss the applicants on the first tier waitlist. Once they come to a consensus, they will offer spots. This will occur continuously as movement occurs until all spots are filled for the incoming class in August. If enough movement occurs this cycle, then they will draw from the second tier etc. So how much movement there is I can't say, but I know I have a good friend from my class that was waitlisted (not sure which tier though) and later got accepted ~May. In terms of what they are looking for, I assume is the same complicated process as they did for your general application. This is complete speculation, but I'd guess that they give each applicant a "score" based on the multi-variable holistic review they do and then those with higher "scores" will be offered first within a tier. But tbh I really don't know and its probably more complicated than that.
But in general, just stay optimistic because there is movement every year!
Also to those that end up not getting an acceptance to OUWB or any other schools, please try to stay positive. I have multiple friends that reapplied and now are in medical school and crushing it. So just because it doesn't go your way this year, you shouldn't forfeit this dream because you are worthy of it. And don't listen to the people who only doubt you, make you doubt yourself, and honestly half the people on SDN. Many of these people are insecure and like to make others feel worse about their applications just to bring themselves up. But they don't know you and your experiences. I applied late in August/September (fyi- I do not advise b/c of rolling admin and also the undue stress of doing that) and if I would have listened to people I wouldn't be an M2 currently.