I was hired per diem originally at my hospital and was oriented 3 days a week (8 hour shifts). Are you doing 12's? If so, that's the same amount I did and I felt it was enough. I was put on my own some shifts 4 weeks into my orientation.....yeah...we have some issues lol. But, if you ask a lot of questions and come home and study up on things you will be fine. If I had a patient with a diagnosis I never heard of, I came home and read all about. Surgical procedure I was unfamiliar with, same thing. I already knew how to do assessments, meds, foleys, Ivs, etc from nursing school
clinical, so job orientation was more important in terms of learning hospital polices and procedures. You say you are a bit rusty with skills, but don't worry...they should walk you through it the first time. Also, I used a skill DVD I had from school and YouTube to look up videos on certain skills I hadn't done in a while that I knew I would be doing on the floor. You say you have a good knowledge base, so that's going to be beneficial.
Good luck! Enjoy being PRN. LOVED it.