It really depends on what they mean by late afternoon. Traffic from Ochsner to the airport is generally pretty bad from 4pm onwards. Ochsner is also pretty out of the way, so I'd expect to have to wait 20-30 minutes to get a cab or even an Uber in that area (although I've never tried, so I could be wrong). Basically, I'd say that if they think you'll be done at 3 or earlier then you'd be OK with a flight at 6. If they think you'll be done by 4, you'd be really pushing it to make a flight at 6. If they think you'll be done later than 4, then I don't think it's going to happen. Expect 45 min or possibly an hour to get from Ochsner to the airport plus whatever time it takes you to get a ride.
As a side note, note that the spelling is "Ochsner", not "Oschner", as I often see people spell it on this board. I'm not affiliated with them, but it's a great, if little known, place with wonderful physicians and a pleasant work environment. Hope you enjoy your interview!