(Duluth, MN)  --  Negotiations continued late into the night Tuesday between the nurses' union and officials at St. Mary's Medical Center in Duluth.  The nurses earlier set a one-day strike date for Tuesday, should talks break down again.  Meanwhile, nurses at nearby St. Luke's Hospital vote today on a tentative contract agreement that their negotiators reached with management after a marathon bargaining session a week ago.  The nurses union recommends its membership approve the contract.  Cindy Prout, a St. Luke's RN on the negotiating team, says the staffing plan in the proposed contract "will help to ensure we will have enough nurses to take care of our patients safely.?