Should take 20 min tops? Lol are you a welder?
I would like to see someone that could jack a car up on a hoist, inspect what work needs to be done, if the entry pipe of the new muffler will even line up to the old one, remove the old rear section, measure what needs to be cut, cut the old exhaust, weld on the new one, adjust it to fit correctly, properly seal the welds, re fit and then get the car off the hoist, all in 20 minutes "tops"
Putting aside your judgement of time; I suggest the drive out to Hampton park and seeing Scotty for the job. He'll get it done good! And it will be better than you hoped