Like Chubs said, a good portion of our class is reapplicants. I applied three times (got in third time). Either they got sick of me applying, or they decided I'd be a good fit (I hope the latter). I didn't get an interview my 2nd year, but made considerable improvements for my third time around and got into several other schools.
Yes, they do rolling admissions. And it varies widely on how long you hear after your interview. I've heard as little as 2 weeks (VERY rare) to as much as 5 months. As far as how long it takes for them to process your secondary, it also depends. What time of year you sent, how many others they are getting in, and generally how motivated they are.
As I've said, and Chubs can attest to, UNC admissions office is realllly slow with pretty much everything. Incredible school though. Well worth the wait.
Good luck.