For some infrequent processes such as a quarterly audit, the systems could be down 90% of the time, but if they work when the audit occurs, then there is no issue. So I generally ask thw process owners to use the "worst case" scenario. So for example, if the application which handles payroll is down, it does down right before it is needed, that is when we would have them evaluate the impact. 

When assessing impacts at intervals, how do you describe "when the impact starts"?

From my experience the most common is the Annual. Another methodology - the first one is a very detailed BIA vs the subsequent iterations of BIAs may be a minor version of the analysis. Any new process that is being covered by the BC strategy will go through the detailed BIA. Any other methodologies adopted?

 Then instructions on rating each critical process as follows: 

I've attached the definitions chart for the primary criteria below.

An aspect of a TIA/BIA that may be overlooked is utility. Utilities such as power, water, and HVAC systems are critical components that support the operational environment of applications. If these utilities fail, they can cause significant disruptions, even if the applications themselves are not directly affected.
While utilities might not directly define RTO (the maximum acceptable length of time that an application can be offline) and RPO (the maximum acceptable amount of data loss measured in time), their failure can impact the ability to meet these objectives. If an application has a stringent RTO or RPO, but the underlying infrastructure (powered by utilities) is unreliable, then the RTO/RPO goals may become unachievable in practice.

Including utility aspects in your assessments ensures that you are planning for resilience at a systemic level, rather than just at the application level.

• Identify Critical Utilities: List all the utilities that support your applications and business processes (e.g., power, water, HVAC, internet connectivity).
  Assess Dependency and Impact: Determine how each utility affects the operations of applications and business processes. Identify the critical dependencies and potential impacts of utility failures.
• Mitigation Strategies: Develop and implement mitigation strategies, such as UPS systems, backup generators, redundant cooling systems, and alternative network connections.
• Integrate into BIA: Include utility failure scenarios in your BIA process. Assess the impact of utility failures on RTO and RPO, and adjust your recovery plans accordingly.

When I ask questions about the applications they use, the records they keep we may achive this organically.

For many most data is self contained within an application (i.e. SaaS).