I would like to provide my personal experience at the Columbus, Ohio office. It was a frustrating experience like any other government office experience.We went there at 7.45 AM. We submitted the application forms and the EAD renewal notices, which the security submitted inside to the USCIS (BCIS ) officers. We were walk-in applicants for interim EADs. It seems that the Columbus office prioritizes "all" the people who have prior appointments before the walk-ins. Therefore, our turn did not come until 12-12.30 PM. We were done in 15-20 minutes after that though. The real smart people actually walked in the office at noon with the interim EAD applications and walked out with us with their Interim EAD cards.
Advise: No point going early if you dont have an appointment. Infact it is wise to walk in during lunch time and get the work done in an hour or hour and a half.