To summarize
You asked about power assurance, not trend or hit checks. 3 places to find this information. HINT: one of is not on this forum.
1. Aircraft maintenance manual- ask your maintenance provider
2. Aircraft flight manual or POH- read it yourself
3. Part 135 or customer operations manual or contract- again read it yourself
You can exceed these requirements if you and your boss agree. You don't want to get fired for being too careful and burning some extra fuel.