Personally if I buy a preowned Rolex I have it rebuilt/services for my own piece of mind. My most recent acquisition I did not. I started to notice it was winding a little rough but still keeping good time and off it went to be rebuilt/serviced.
http://www.dstimeservice.com/
Otherwise, 5-7 years seems to be a good recommendation however, some people just let them run and don't have service done... Really up to you and what you are comfortable with.