Depends on what's wrong with it and how it's going to be solved. On Chrysler products, which I have more experience on, it takes about an hour to replace an outer joint or boot. A new joint costs a lot more than a rebuilt half shaft. A special tool is needed on GM's outer boots, and another one is needed to release the joint from the shaft to replace the boot. Those tools are not expensive but extra time is needed. An experienced mechanic will still have a joint replaced in about an hour.