I am a registered nurse working in a public hospital. The ward I work in has a staffing arrangement of 6 nursing hours per patient day (NHPPD). Often, however, absences are filled by casuals working a shift of shorter duration. Is that right?

No. Clause 53 (Staffing Arrangements) of the Public Health System Nurses’ and Midwives’ (State) Award 2017 talks about the requirements to backfill an absence. Where an absence is to be filled to maintain the required NHPPD, the default position requires that it be fully backfilled and not partially backfilled (for example, an absence that creates an 8.5 hour vacancy should, as a default, be filled with an 8.5-hour replacement).