How long does it take to replace the catalyst converter

If all goes well, about an hour or so. But We are talking about a system that is exposed to the elements on-top-of being extremely hot, so it expands & contracts constantly, which can cause things to seize. The condition of the bolts that hold it to the engine can sometimes be a problem. Especially if someone installed studs in the past 12 years in place of nuts & bolts. Studs may need a torch to heat the manifold, or the securing nuts to release it. But studs that have rusted & rotted very thin have a tendency of snapping. For some , that can run into headaches. If it is a nut & bolt, they can just be cut with a torch & a new pair installed. SEE: https://www.flickr.com/photos/127907981@N06/15567674375/ The condition of the pipe that is removed from the other end of it is also a concern. If that is rotted , then that will need replacing. SEE: https://www.flickr.com/photos/127907981@N06/14946956234/ Also, the Oxygen sensor needs to be removed. Most times they come out with little problems , but again every so often you have one that is just fused into the converter. I ran into that problem a few weeks ago with a 1997 Altima pipe. That bugger didn't want to come out. When converters get hot , they can get hot. If the engine had ever had needed of a tune up desperately where the engine was misfiring , this could cause the converter to get much hotter. RED hot But if it's on a lift being done by someone who does it all the time and has a torch if he needs it, and things go smooth , An Hour to 90 minutes TOPS