Always give at least a minimum of a two week notice before leaving, sometimes its longer depending on the situation. Always try and leave, if possible on good terms with any place of employment; you never know who you will have to work with again. The assignment as you describe it sounds like a decent one to learn with. It takes time to gain speed and proficiency. Ltc/snfs are not bad places to start as they help to find a routine and a system that works for you. It also helps you to learn time management skills.
The orientation period sounds short, in my area the minimum would be a couple weeks. I started in the same type of setting than moved onto med-surg/tele and then moved into critical care. Best advice is to remember you are brand new and need time to learn the process.