The scenes take as long as you are willing to spend dollars for or as long as your performers are REALLY able to perform. Real performers can pull it off in a short amount of time because they get you the specific stuff you need and go home. Other times an actress will only put out as much as her agent tells her to or she will expect more money. They are basically no fun and don't appear to like sex enough to be in it for the pleasure. But there are plenty out there like them. It's a business, and not quite as much fun as it use to be.