Howdy
Interview is about 20-30 minutes long. Interview panel can comprise of various people from the chief pilot, chief training and various senior training captains. they will ask you some questions on 737 if you fly it. If not then you may get some questions on the aircraft you do fly if they are familiar with it. Some guys are asked about airport signage, runway and taxiway markings, high speed flight, ETOPS requirements, LVP's and LVTO.
Nothing nasty about it as long as you prepare. They are pretty reasonable.
Good luck