I am assuming that you are a Captain going for the AIC interview. Your carrier should give you a "briefing" which will be 1-2 days, covering the ops manual, company manual, route structure and FDTL (flight duty time limits).
You DGCA interview will last anywhere from 5 mins (mine) to 45 mins, depending on how you present yourself and your background. Take all your log books, licenses and medical. The FDTL has just changed so make sure you have a basic knowledge of the new regs. Good luck. 90 days after you first join you also have to take a 50 question multiple choice Air Regulations exam. Good luck!