Final answer:
The amount of time required to retain nursing schedules is not specified in the provided information and can vary by jurisdiction or institution; this typically ranges from 1 to 7 years, depending on regulatory or institutional requirements.
Step-by-step explanation:
The question about the amount of time required to retain nursing schedules does not directly relate to any provided reference information related to a survey of nurses' experiences or disease proportions — it seems to be an administrative or regulatory question, likely dealing with labor or healthcare regulations. Generally, the length of time for which medical records or nurse scheduling records must be kept can vary by institution and jurisdiction. It's important to consult the relevant regulations in your specific area or health institution. However, this requirement often ranges from 1 to 7 years, and in some cases, it can be longer, especially if the records might be needed for legal reasons or for long-term studies of staffing patterns or health outcomes.