Depends if you are hired full time or part time. If it is full time, it is most likely whenever the office is open. If it is part time it could be anywhere from 1-4 days a week depending on the Pediatritian(s) you work for.
Varies by institution. Some RN's work 3 12's, then have 2 days off - others work 4 10's then have 2 days off. RN's continually rotate days off in that manner - rarely will only but the topmost RN...