I've done it twice. The first time was on my 07 convertible that is a low mileage garage queen. It was done in less than an hour. What took the most time for me was getting the second rubber hanger back in place. The second time was on my son's 04 which had a lot of miles on it. The flange bolt studs were rusty and broke off when we tried to remove them. It was necessary to drill out what was left of the studs on the cat side of the flange, and then use new stainless steel bolts.

I did not take this photo, but it shows how the bolts can break off if they are badly rusted. In this case I think who removed it may have actually used a saw to cut them off. Drilling out the holes on the cat side of the flange was not that difficult.