Skyrender - to echo what Gabe said, about an hour, did them in my garage after putting car(s) up on ramps.
Once you install them, you just use one hand to direct the jack to where on the rail you want the car lifted from and use the other hand to pump the jack. Then you can put your jack stands anywhere along the rail. If you have a quick pump jack, you can literally have one side completely up in the air 10 seconds, without having to get down on your hands and knees and figure out where the normal jacking points are, carefully placing your hockey pucks/lifting blocks, place you jack in the right place, etc.
