I am in the middle of a 12 week orientation. Before I was hired I was in contact with a large teaching hospital that also had a 12 week program. I think the reason my orientation lasts as long as it does is because our RN to Pt ratio can run high and that I'm a float. Oh and that 12 weeks can be cut short if we are up to par.
When I was new grad, I was on orientation for 20 weeks. During that time we did classes a couple of days a week and a couple of days on the floor. There were some people who were ready to get off orientation early and some who wanted to be on longer. The nice thing with the program that I was in, was that we floated with our preceptors to floors that we might float to when off orientation. Also it was nice because we changed preceptors every 6 weeks.