About an hour tops, but never rush a job

Spray all the bolts down with something to loosen them up, WD40 PB etc. Remove the two bolts joining flex/cat pipe to mid pipe. Pop hood, remove Heat shield then unbolt the 4 bolts holding cat. to man. Make sure you suport the cat section with a friend or jack stand. You will need a gasket at both ends of the cat. section.
Hope this helps
JD