I have never heard of any such requirement but like Kathyang I have seen studies indicating that anything over 10 hours was not a good thing. The last 14 months I worked is was Friday, Saturday and Sunday from 1800 to 0600. It was a small hospital and I was not consistently busy by any stretch of the imagination but I can tell you that the last 2 hours were the most difficult. That may have be age related more than anything else. Having spent many years in facilities where the nurses in the most critical areas (ICU and ER) work 12 hours shifts, most of the nurse related mistakes I had to deal with as Transfusion Supervisor were with those nurses.