During post-incident review is the best time to update the incident response plan after observing several deficiencies in the current plan while responding to a high-profile security incident. A post-incident review is a process of analyzing and evaluating the incident response activities, identifying the lessons learned, and documenting the recommendations and action items for improvement. Updating the incident response plan during post-incident review helps to ensure that the plan reflects the current best practices, addresses the gaps and weaknesses, and incorporates the feedback and suggestions from the incident response team and other stakeholders. Therefore, during post-incident review is the correct answer.
References:
* https://www.cisa.gov/sites/default/files/publications/Incident-Response-Plan-Basics_508c.pdf
* https://www.techtarget.com/searchsecurity/feature/5-critical-steps-to-creating-an-effective-incident- response-plan
* https://www.integrify.com/blog/posts/incident-response-plan-need-an-update/

According to the CISM Manual, the organization's risk appetite is the amount and type of risk that the organization is willing to accept in order to achieve its objectives1. The organization's risk appetite should guide the development and maintenance of an information security program, as it determines the level of security controls, resources, and activities that are needed to protect the organization's assets and operations1.
The CISM Manual states that "the information security program should be aligned with the organization's risk appetite, which reflects its tolerance for risk and its strategic objectives" (IR 8288A)1. The information security program should also consider other factors that influence the organization's risk appetite, such as its mission, vision, values, culture, stakeholders, regulations, standards, guidelines, and best practices1.
The CISM Manual also provides guidance on how to develop and maintain an information security program based on the organization's risk appetite. It recommends using a process that involves identifying, analyzing, evaluating, treating, monitoring, and reviewing risks that affect the organization's information assets1. It also suggests using a framework or model that supports the development of an information security program based on the organization's risk appetite (e.g., ISO/IEC 27001)1.
References: 1: IR 8288A - Information Security Program Development | CSRC NIST