"How long" depends on a number of factors, including if the vehicle is on the lift or being done on the ground, availability of proper tools for the job, experience of the person doing the job. Normally, a shop would quote about 1.5-2.0 hours for the job, not including wheel alignment. If I was doing the job at home and my impact gun wasn't working to remove the nut, I would spray rust penetrent on the nut and let it soak. I would use a long, 1/2" drive breaker bar and 6-point deep socket. If that wasn't enough to break it loose, I'd put a length of pipe on the breaker bar to give more leverage. If I needed more than that, I would use a torch to heat the nut up and then try the breaker bar and socket.