Greekgrrl is right on. If the chapter didn't meet quota or is below total, they can extend COB bids whenever they want; it doesn't have to follow a formal COB rush week or anything.
If they're interested and can extend COBs, they'll probably make sure you meet a bunch of the sisters. Then they'll go through whatever membership selection process they have to decide whether to extend you a bid. If you get a bid, they may do a special new member education period just for you, or have you hold off if they're planning a spring rush.
As for what to talk about, just relax and be yourself. Have some questions about the sorority ready to ask. Do your homework... all the advice we normally give PNMs for formal recruitment
Good luck!