1. September OCI is mostly smaller firms, many with only Atlanta or SE offices (there are exceptions, but this is just the general rule). All the bigger, national firms do their interviewing in August.
2. Call career services and explain your situation and ask. They're all very nice, and I'm sure they've seen this situation before. I don't know of anyone who missed the deadline and actually wanted to interview, so I don't have an answer. Sorry!